Dicarboxylic diester, process for producing the same, and refrigerating machine lubricating oil comprising the ester

ABSTRACT

A diester represented by the formula  
                 
 
wherein A represents a cyclohexane ring, cyclohexene ring or benzene ring, X is H or methyl group, R X  and R Y  are the same or different and each is C3-C18 branched-chain alkyl group, C1-C18 straight-chain alkyl group, C2-C18 straight-chain alkenyl or C3-C18 cycloalkyl, provided that when A is a benzene ring, R X  and R Y  are different from each other and —COOR X  and —COOR Y  are attached to two adjacent carbon atoms of the benzene ring, and having the following properties: 
1) a total acid number of 0.05 mgKOH/g or less, 2) a sulfated ash content of 10 ppm or less, 3) a sulfur content of 20 ppm or less, 4) a phosphorus content of 20 ppm or less, 5) a peroxide value of 1.0 meq/kg or less, 6) a carbonyl value of 10 or less; 
     7) a volume resistivity of 1×10 11  Ω·cm or more, 8) a hydroxyl value of 3 mgKOH/g or less, and 9) a water content of 100 ppm or less, a process for preparing the same and a refrigerator lubricating oil comprising the diester.

FIELD OF THE INVENTION

The present invention relates to an alicyclic dicarboxylic acid diestersuitable as a lubricating oil for a refrigerator and a process forpreparing the same.

Furthermore, the present invention concerns with an alicyclic oraromatic adjacent dicarboxylic acid mixed diester prepared by a 2-stepprocess, the ester being useful as a lubricating oil (hereinafterreferred to as “refrigerator oil”) for compressors in automotive airconditioners, refrigerators, room air conditioners, large-sizeindustrial refrigerators or the like using hydrofluorocarbonrefrigerants, a process for preparing the same and a refrigerator oilcontaining the ester.

The term “alicyclic or aromatic adjacent dicarboxylic acid mixeddiester” used in this specification and claims refers to an alicyclic oraromatic dicarboxylic acid diester wherein the two ester groups thereofare attached to two adjacent carbon atoms of the alicyclic or aromaticgroup such as cyclohexane, cyclohexene or benzene, the two ester groupsbeing different from each other.

PRIOR ART

In recent years, an attempt is going on to substitute a refrigerant suchas HFC-134a which is a hydrofluorocarbon (HFC) for R11 or R12 which is achloro-fluorocarbon (CFC) or R22 which is a hydrochloro-fluorocarbon(HCFC) to overcome the problems of ozone layer depletion and globalwarming. Now oxygen-containing synthetic oils have come into use as arefrigerator oil for HFC. Examples are polyol esters (JP-A-3-128991,JP-A-3-200895, etc.), polyvinyl ethers (JP-A-6-128578, etc.) andpolyalkylene glycol (JP-A-2-242888, JP-A-3-33193, etc.).

WO 97/21792 discloses that an alicyclic dicarboxylic acid diesteravailable as a new type of ester has a high hydrolysis stability and canbe used as a metal cutting fluid or as a refrigerator oil.

More recently, however, the critical mind toward global warming hasbecome intensified so that the development of efficient machinery is onthe way to save energy in refrigerators for the purpose of reducing theemission level of carbon dioxide which causes global warming. On theother hand, since a CFC substitute itself (CFC and HCFC substitutes),used as a refrigerant, is one of global warming substances, it isdesired to decrease the quantity of the refrigerant to be used. Toimprove the efficiency of machinery and to decrease the refrigerantconsumption, a compact machinery may be a candidate for achieving thegoals. In compact machinery, however, lubricating oils will be usedunavoidably under severer conditions. Therefore, new refrigerator oilsneed to be improved over conventional oils in hydrolysis stability, heatstability, electrical insulating property, lubricity and the like. Yetnew refrigerator oils which can meet these requirements have not beendeveloped. Thus, there is a need for providing an alicyclic dicarboxylicacid diester which is suitable as a refrigerator oil and which has animproved performance.

Generally a refrigerator oil is selected considering whether it has aviscosity characteristic suitable for a particular apparatus to be used.For example, JIS-K-2211 classifies refrigerator oils into fivecategories. Thus, various refrigerator oils having different viscositiesare necessary for different apparatuses and for different intended uses.

At the moment, polyol ester refrigerator oils are available forpractical applications. Viscosity adjustment of such refrigerator oilsis carried out by (1) mixing at least 2 kinds of polyol esters ofdifferent viscosities or by (2) providing a polyol mixed ester of thedesired viscosity in a 1-step process using a mixture of at least twoalcohols or acids as the starting materials for esterification, asdisclosed, for example, in JP-A-3-200895 and JP-A-4-20597.

WO 97/21792 discloses, as mentioned above, that an alicyclic adjacentdicarboxylic acid ester available as a new type of ester has anexcellent hydrolysis stability and can be used as a metal cutting fluidor as a refrigerator oil. JP-A-4-226193 describes an aromatic adjacentdicarboxylic acid ester has a high performance as a refrigerator oil.

DISCLOSURE OF THE INVENTION

In view of the foregoing, a first object of the present invention is toprovide a process for preparing a dicarboxylic acid diester which isexcellent in hydrolysis stability, heat stability, electrical insulatingproperty, lubricity and the like.

Furthermore, the present inventors intensively investigated alicyclicdicarboxylic acid esters in an attempt to cope with the need for variousviscosity grades of refrigerator oils, and found that when the viscosityadjustment is carried out by mixing at least two alicyclic adjacentdicarboxylic acid esters of different viscosities according to method(1) above, the obtained ester mixture may be inferior in stability,electrical insulating property, lubricity, miscibility withrefrigerants, etc. due to the drawbacks of low-viscosity esters orhigh-viscosity esters. On the other hand, the inventors discovered thatalicyclic adjacent dicarboxylic acid mixed diesters can cope with theneed for refrigerator oils of various viscosity grades. However, when amixed diester is prepared by method (2) above, the obtained diester isnot satisfactory in stability, electrical insulating property, lubricityand the like when used under recent stricter conditions, because thequality of the mixed diester is low due to low reactivity inesterification.

In this situation, a second object of the present invention is toprovide a process for preparing a mixed diester which, when used as arefrigerator oil, is easily adjustable to a wide range of viscositiesand which is excellent in hydrolysis stability, heat stability,electrical insulating property and lubricity.

The present inventors conducted extensive research to achieve theforegoing objects and found that alicyclic dicarboxylic acid diesters oralicyclic or aromatic adjacent dicarboxylic acid mixed diesters havingspecific properties are outstanding in hydrolysis stability, heatstability, electrical insulating property, lubricity and the like.

The present invention provides an ester (or a refrigerator lubricatingoil comprising said ester), said ester being selected from the groupconsisting of alicyclic or aromatic adjacent dicarboxylic acid diestersrepresented by the formula (E)

wherein A represents a cyclohexane ring, a cyclohexene ring or a benzenering, X is a hydrogen atom or methyl, R^(X) and R^(Y) are the same ordifferent and each is a branched-chain alkyl group having 3 to 18 carbonatoms, a straight-chain alkyl group having 1 to 18 carbon atoms, astraight-chain alkenyl group having 2 to 18 carbon atoms or a cycloalkylgroup having 3 to 10 carbon atoms, with the proviso that when A is abenzene ring, R^(X) and R^(Y) are different from each other and thegroup —COOR^(X) and the group —COOR^(Y) are attached to two adjacentcarbon atoms of the benzene ring, said ester (or said refrigeratorlubricating oil) having the following properties:

-   -   1) a total acid number: 0.05 mgKOH/g or less;    -   2) a sulfated ash content: 10 ppm or less;    -   3) a sulfur content: 20 ppm or less;    -   4) a phosphorus content: 20 ppm or less;    -   5) a peroxide value: 1.0 meq/kg or less;    -   6) a carbonyl value: 10 or less;    -   7) a volume resistivity: 1×10¹¹ Ω·cm or more;    -   8) a hydroxyl value: 3 mgKOH/g or less, and    -   9) a water content: 100 ppm or less.

The alicyclic or aromatic dicarboxylic acid diesters represented by theformula (E) include alicyclic dicarboxylic acid diesters represented bythe formula (1)

wherein A represents a cyclohexane ring or cyclohexene ring, X is ahydrogen atom or methyl, R¹ and R² are the same or different and each isa branched-chain alkyl group having 3 to 18 carbon atoms, astraight-chain alkyl group having 1 to 18 carbon atoms, a straight-chainalkenyl group having 2 to 18 carbon atoms or a cycloalkyl group having 3to 10 carbon atoms, as well as alicyclic or aromatic adjacentdicarboxylic acid mixed diesters represented by the formula (4)

wherein A represents a cyclohexane ring, a cyclohexene ring or a benzenering, X is a hydrogen atom or methyl, R⁵ and R⁶ are different and eachis a branched-chain alkyl group having 3 to 18 carbon atoms, astraight-chain alkyl group having 1 to 18 carbon atoms, a straight-chainalkenyl group having 2 to 18 carbon atoms or a cycloalkyl group having 3to 10 carbon atoms, and groups —COOR⁵ and —COOR⁶ are attached to twoadjacent carbon atoms of the cyclohexane, cyclohexene or benzene ringrepresented by A.

According to the inventors' research, it was discovered that thealicyclic dicarboxylic acid diester represented by the formula (1) andthe alicyclic or aromatic adjacent dicarboxylic acid mixed diesterrepresented by the formula (4) prepared by specific processes have theproperties 1) to 9) described above, and are excellent in hydrolysisstability, heat stability, electrical insulating property, lubricity andthe like.

Especially, the present inventors conducted extensive research toachieve the foregoing first object and found that an ester prepared byesterification or ester interchange reaction using an alcohol havingspecific properties and a specific catalyst has an excellent hue andexhibits excellent electrical insulating property, heat stability andlong-term hydrolysis stability when used as a refrigerator oil, andtherefore can provide a refrigerator oil having remarkably highperformance compared with conventional refrigerator oils. Based on thesenovel findings, the inventions described below in items 1 to 4 werecompleted.

Thus, the present invention relates to the following inventions.

Item 1. An alicyclic dicarboxylic acid diester (or a refrigeratorlubricating oil comprising the alicyclic dicarboxylic acid diester), theester being represented by the formula (1)

wherein A¹ represents a cyclohexane ring or cyclohexene ring, X is ahydrogen atom or methyl, R¹ and R² are the same or different and each isa branched-chain alkyl group having 3 to 18 carbon atoms, astraight-chain alkyl group having 1 to 18 carbon atoms, a straight-chainalkenyl group having 2 to 18 carbon atoms or a cycloalkyl group having 3to 10 carbon atoms; the alicyclic dicarboxylic acid diester (or therefrigerator lubricating oil comprising the alicyclic dicarboxylic aciddiester) having the following properties:

-   -   1) a total acid number of 0.05 mgKOH/g or less,    -   2) a sulfated ash content of 10 ppm or less,    -   3) a sulfur content of 20 ppm or less,    -   4) a phosphorus content of 20 ppm or less,    -   5) a peroxide value of 1.0 meq/kg or less,    -   6) a carbonyl value of 10 or less,    -   7) a volume resistivity of 1×10¹¹ Ω·cm or more,    -   8) a hydroxyl value of 3 mgKOH/g or less, and    -   9) a water content of 100 ppm or less.

It is preferable that the alicyclic dicarboxylic acid diester (or therefrigerator lubricating oil comprising the alicyclic dicarboxylic aciddiester) further has a hue of 50 or less (as measured according toJIS-K-0071-1-1998).

Item 2. A process for preparing alicyclic dicarboxylic acid diesterrepresented by the formula (1)

wherein A¹ represents a cyclohexane ring or cyclohexene ring, X is ahydrogen atom or methyl, R¹ and R² are the same or different and each isa branched-chain alkyl group having 3 to 18 carbon atoms, astraight-chain alkyl group having 1 to 18 carbon atoms, a straight-chainalkenyl group having 2 to 18 carbon atoms or a cycloalkyl group having 3to 10 carbon atoms; and having the following properties:

-   -   1) a total acid number of 0.05 mgKOH/g or less,    -   2) a sulfated ash content of 10 ppm or less,    -   3) a sulfur content of 20 ppm or less,    -   4) a phosphorus content of 20 ppm or less,    -   5) a peroxide value of 1.0 meq/kg or less,    -   6) a carbonyl value of 10 or less,    -   7) a volume resistivity of 1×10¹¹ Q-cm or more,    -   8) a hydroxyl value of 3 mgKOH/g or less, and    -   9) a water content of 100 ppm or less,        the process comprising the steps of

-   (i) subjecting    -   a) an alicyclic dicarboxylic acid represented by the formula (2)    -    wherein A¹ and X are as defined above, or an anhydride thereof,        and

-   b) an aliphatic monohydric alcohol having 1 to 18 carbon atoms or an    alicyclic monohydric alcohol having 3 to 10 carbon atoms each having    a peroxide value of 1.0 meq/kg or less    to esterification reaction in the absence of a catalyst or in the    presence of a sulfur-free and phosphorus-free catalyst, or    subjecting

-   a′) an alicyclic dicarboxylic acid diester represented by the    formula (3)

-    wherein A¹ and X are as defined above, R³ and R⁴ are the same or    different and each is a branched-chain alkyl group having 3 or 4    carbon atoms or a straight-chain alkyl group having 1 to 4 carbon    atoms, and

-   b′) an aliphatic monohydric alcohol of 5 to 18 carbon atoms or an    alicyclic monohydric alcohol of 3 to 10 carbon atoms each having a    peroxide value of 1.0 meq/kg or less    to ester interchange reaction in the absence of a catalyst or in the    presence of a sulfur-free and phosphorus-free catalyst,    to thereby obtain a reaction mixture containing the diester    represented by the formula (1),

-   (ii) removing excess starting materials from the reaction mixture    obtained in step (i) to thereby obtain the diester in a crude form,

-   (iii) neutralizing the crude diester obtained in step (ii) and    washing the neutralized crude diester with water,

-   (iv) purifying the crude diester neutralized and washed with water    in step (iii) by treatment with 1 to 4 kinds of adsorbents, and

-   (v) dehydrating the diester purified in step (iv).

Item 3. A refrigerator lubricating oil comprising the alicyclicdicarboxylic acid diester represented by the formula (1) and havingproperties 1)-9) according to item 1 above.

Item 4. A refrigerator lubricating oil comprising the alicyclicdicarboxylic acid diester represented by the formula (1) and havingproperties 1) to 9) and obtainable by the process according to item 2.

It is preferable that in the refrigerator lubricating oil of item 4, thealicyclic dicarboxylic acid diester represented by the formula (1)contained in said lubricating oil is an ester obtained by carrying outthe esterification in an inert gas atmosphere or in an inert gas stream.

In the specification, the inventions as defined above in Items 1 to 4and the inventions relating to the alicyclic dicarboxylic acid diestersof the formula (1) are referred to as “embodiment I”.

Furthermore, the present inventors conducted intensive investigations toachieve said second object using the foregoing alicyclic adjacentdicarboxylic acid mixed diester represented by the formula (4) as anrefrigerator oil. We discovered that when a 2-step esterificationprocess is carried out in preparing the alicyclic adjacent dicarboxylicacid mixed diester, a high-quality mixed diester can be produced undermild conditions and that when the obtained mixed diester is used as arefrigerator oil, it can be easily adjusted to a wide range ofviscosities and it is excellent in hydrolysis stability, heat stability,electrical insulating property and lubricity. Moreover, the presentinventors found that when this technique is applied for preparing thearomatic adjacent dicarboxylic acid mixed diester, the same effects canbe produced. After carrying out further investigation, the inventorscompleted the inventions as defined in Items 5 to 9 to be describedbelow.

Item 5. An alicyclic or aromatic adjacent dicarboxylic acid mixeddiester (or a refrigerator lubricating oil comprising said alicyclic oraromatic adjacent dicarboxylic acid mixed diester) represented by theformula (4)

wherein A represents a cyclohexane ring, a cyclohexene ring or a benzenering, X is a hydrogen atom or methyl, R⁵ and R⁶ are different from eachother and each is a branched-chain alkyl group having 3 to 18 carbonatoms, a straight-chain alkyl group having 1 to 18 carbon atoms, astraight-chain alkenyl group having 2 to 18 carbon atoms or a cycloalkylgroup having 3 to 10 carbon atoms, and group —COOR⁵ and group —COOR⁶ areattached to two adjacent carbon atoms of the cyclohexane, cyclohexene orbenzene ring, the ester (or the refrigerator lubricating oil) having thefollowing properties:

-   -   1) a total acid number: 0.05 mgKOH/g or less;    -   2) a sulfated ash content: 10 ppm or less;    -   3) a sulfur content: 20 ppm or less;    -   4) a phosphorus content: 20 ppm or less;    -   5) a peroxide value: 1.0 meq/kg or less;    -   6) a carbonyl value: 10 or less;    -   7) a volume resistivity: 1×10¹¹ Ω·cm or more;    -   8) a hydroxyl value: 3 mgKOH/g or less; and    -   9) a water content: 100 ppm or less.

Item 6. An ester mixture of

-   -   (1) an alicyclic or aromatic adjacent dicarboxylic acid di(lower        alkyl)ester represented by the formula (7)    -    wherein A represents a cyclohexane ring, a cyclohexene ring or        a benzene ring, X is a hydrogen atom or methyl, and R^(5a) is a        branched-chain alkyl group having 3 to 5 carbon atoms, a        straight-chain alkyl group having 1 to 5 carbon atoms, a        straight-chain alkenyl group having 2 to 5 carbon atoms or a        cycloalkyl group having 3 to 5 carbon atoms, and the two        —COOR^(5a) groups are the same and attached to two adjacent        carbon atoms of the cyclohexane, cyclohexene or benzene ring        represented by A;    -   (2) an alicyclic or aromatic adjacent dicarboxylic acid mixed        diester represented by the formula (4a)    -    wherein A and X are as defined in the formula (7), and R^(5a)        and R^(6a) are different from each other and R^(5a) is as        defined in the formula (7), and R^(6a) is a branched-chain alkyl        group having 6 to 18 carbon atoms, a straight-chain alkyl group        having 6 to 18 carbon atoms, a straight-chain alkenyl group        having 6 to 18 carbon atoms or a cycloalkyl group having 6 to 10        carbon atoms, and the group —COOR^(5a) and the group —COOR^(6a)        are attached to two adjacent carbon atoms of the cyclohexane,        cyclohexene or benzene ring represented by A, and    -   (3) an alicyclic or aromatic adjacent dicarboxylic acid        di(higher alkyl)ester represented by the formula (8)    -    wherein A, X and R^(6a) are as defined in the formula (4a), and        the two —COOR⁶ groups are the same and attached to two adjacent        carbon atoms of the cyclohexane, cyclohexene or benzene ring        represented by A,        the ester mixture having the following properties:    -   1) a total acid number of 0.05 mgKOH/g or less,    -   2) a sulfated ash content of 10 ppm or less,    -   3) a sulfur content of 20 ppm or less,    -   4) a phosphorus content of 20 ppm or less,    -   5) a peroxide value of 1.0 meq/kg or less,    -   6) a carbonyl value of 10 or less,    -   7) a volume resistivity of 1×10¹¹ Ω·cm or more,    -   8) a hydroxyl value of 3 mgKOH/g or less, and    -   9) a water content of 100 ppm or less.

Item 7. A process for preparing an alicyclic or aromatic adjacentdicarboxylic acid mixed diester or an ester mixture, wherein thealicyclic or aromatic adjacent dicarboxylic acid mixed diester isrepresented by the formula (4)

wherein A represents a cyclohexane ring, a cyclohexene ring or a benzenering, X is a hydrogen atom or methyl, R⁵ and R⁶ are different from eachother and each is a branched-chain alkyl group having 3 to 18 carbonatoms, a straight-chain alkyl group having 1 to 18 carbon atoms, astraight-chain alkenyl group having 2 to 18 carbon atoms or a cycloalkylgroup having 3 to 10 carbon atoms (particularly, R⁵ is a straight-chainalkyl group having 1 to 5 carbon atoms or a branched-chain alkyl grouphaving 3 to 5 carbon atoms, R⁶ is a straight-chain or branched-chainalkyl group having 6 to 11 carbon atoms), and the group —COOR⁵ and thegroup —COOR⁶ are attached to two adjacent carbon atoms of thecyclohexane, cyclohexene or benzene ring represented by A; and saidester mixture is a mixture of

-   -   (1) an alicyclic or aromatic adjacent dicarboxylic acid di(lower        alkyl)ester represented by the formula (7)        wherein A and X are as defined in the formula (4), and R^(5a)        represents a branched-chain alkyl group having 3 to 5 carbon        atoms, a straight-chain alkyl group having 1 to 5 carbon atoms,        a straight-chain alkenyl group having 2 to 5 carbon atoms or a        cycloalkyl group having 3 to 5 carbon atoms, and the two        —COOR^(5a) groups are the same and attached to two adjacent        carbon atoms of the cyclohexane, cyclohexene or benzene ring        represented by A,    -   (2) an alicyclic or aromatic adjacent dicarboxylic acid mixed        diester represented by the formula (4a)    -    wherein A and X are as defined in the formula (7), and R^(5a)        and R^(6a) are different from each other and R^(5a) is as        defined above, and R^(6a) is a branched-chain alkyl group having        6 to 18 carbon atoms, a straight-chain alkyl group having 6 to        18 carbon atoms, a straight-chain alkenyl group having 6 to 18        carbon atoms or a cycloalkyl group having 6 to 10 carbon atoms,        and the group —COOR^(5a) and the group —COOR^(6a) are attached        to two adjacent carbon atoms of the cyclohexane, cyclohexene or        benzene ring represented by A, and    -   (3) an alicyclic or aromatic adjacent dicarboxylic acid        di(higher alkyl)ester represented by the formula (8)    -    wherein A, X and R^(6a) are as defined in the formula (4a), and        the two —COOR^(6a) groups are the same and attached to two        adjacent carbon atoms of the cyclohexane, cyclohexene or benzene        ring represented by A, and        wherein the alicyclic or aromatic adjacent dicarboxylic acid        diester or the ester mixture has the following properties:    -   1) a total acid number of 0.05 mgKOH/g or less,    -   2) a sulfated ash content of 10 ppm or less,    -   3) a sulfur content of 20 ppm or less,    -   4) a phosphorus content of 20 ppm or less,    -   5) a peroxide value of 1.0 meq/kg or less,    -   6) a carbonyl value of 10 or less,    -   7) a volume resistivity of 1×10¹¹ Ω·cm or more,    -   8) a hydroxyl value of 3 mgKOH/g or less, and    -   9) a water content of 100 ppm or less,        the process comprising the steps of

-   (i) (a) subjecting an alicyclic or aromatic adjacent dicarboxylic    acid anhydride represented by the formula (5s)    -   wherein A and X are as defined above and “alcohol component 1”        (namely, a single alcohol or alcohol mixture comprising a        monohydric alcohol having 1 to 5 carbon atoms (P) and a        monohydric alcohol having 6 to 18 carbon atoms (Q) wherein        (P):(Q) is 0.1:99.9 to 100:0 (molar ratio)) to esterification        reaction to thereby give an alicyclic or aromatic adjacent        dicarboxylic acid monoester represented by the formula (5)    -   wherein A, X and R⁵ are as defined above, and the group —COOR⁵        and the group —COOH are attached to two adjacent carbon atoms of        the cyclohexane, cyclohexene or benzene ring represented by A,    -   (b) subjecting the alicyclic or aromatic adjacent dicarboxylic        acid monoester represented by the formula (5) obtained in        step (a) and “alcohol component 2” (namely, a single alcohol or        alcohol mixture comprising a monohydric alcohol having 1 to 5        carbon atoms (S) and a monohydric alcohol having 6 to 18 carbon        atoms (T) wherein (S):(T) is 0:100 to 99.9:0.1 (molar ratio)) to        a further esterification reaction in the absence of a catalyst        or in the presence of a sulfur-free and phosphorus-free catalyst    -   to thereby give a reaction mixture containing said ester mixture        of (1) the alicyclic or aromatic adjacent dicarboxylic acid        di(lower alkyl)ester represented by the formula (7), (2) the        alicyclic or aromatic adjacent dicarboxylic acid mixed diester        represented by the formula (4a), and (3) the alicyclic or        aromatic adjacent dicarboxylic acid di(higher alkyl)ester        represented by the formula (8),

-   (ii) removing excess starting materials from the reaction mixture    obtained in step (i) to thereby obtain the ester mixture in a crude    form,

-   (iii) neutralizing the crude diester obtained in step (ii) and    washing the neutralized crude diester with water,

-   (iv) purifying the crude diester neutralized and washed with water    in step (iii) by treatment with 1 to 4 kinds of adsorbents,

-   (v) dehydrating the diester purified in step (iv) to thereby give    the ester mixture having the properties 1) to 9), and if desired,

-   (vi) separating the aromatic adjacent dicarboxylic acid mixed    diester-mixture represented by the formula (4a) from the obtained    ester mixture to thereby give the alicyclic or aromatic adjacent    dicarboxylic acid mixed diester represented by the formula (4).

Item 8. A refrigerator lubricating oil comprising the alicyclic oraromatic adjacent dicarboxylic acid mixed diester represented by theformula (4) having the properties 1) to 9) of Item 5 above or the estermixture having properties 1) to 9) of Item 6 above.

Item 9. A refrigerator lubricating oil comprising the alicyclic oraromatic adjacent dicarboxylic acid mixed diester represented by theformula (4) having properties 1) to 9) or the ester mixture havingproperties 1) to 9), which is obtainable by the process of Item 7.

It is preferable that in the refrigerator lubricating oil of item 9, thealicyclic or aromatic adjacent dicarboxylic acid mixed diester or theester mixture represented by the formula (4) contained in saidlubricating oil is the ester prepared by carrying out the esterificationreactions in steps (a) and (b) in an inert gas atmosphere or in an inertgas stream.

In the specification, the inventions as defined above in Items 5 to 9and the inventions relating to the process for preparing the abovealicyclic or aromatic adjacent dicarboxylic acid mixed diester and therefrigerator oil containing said mixed diester are referred to as“embodiment II”.

Described below are the esters of embodiment I, processes for preparingthe same, the esters of embodiment II, processes for preparing the same,methods for purification of esters according to embodiments I and II,and then lubricating oils for refrigerators (hereinafter referred to as“refrigerator oils”) which contain these esters.

Esters of Embodiment I and Process for Preparation Thereof

Alicyclic Dicarboxylic Acid Diester Represented by the Formula (1)

The alicyclic dicarboxylic acid diester represented by the formula (1)according to the invention (hereinafter sometimes called “presentester”)

wherein A¹ represents a cyclohexane ring or cyclohexene ring, X is ahydrogen atom or methyl, R¹ and R² are the same or different and each isa branched-chain alkyl group having 3 to 18 carbon atoms, astraight-chain alkyl group having 1 to 18 carbon atoms, a straight-chainalkenyl group having 2 to 18 carbon atoms or a cycloalkyl group having 3to 10 carbon atoms, can be prepared by esterifying a) an acid componentand b) an alcohol component in the conventional manner, preferably in anatmosphere of inert gas such as nitrogen in the absence of a catalyst orin the presence of a sulfur-free and phosphorus-free catalyst withstirring and heating.

The acid component as component a) for use in the esterificationincludes the alicyclic dicarboxylic acid represented by the formula (2)or an anhydride thereof, or an alicyclic dicarboxylic acid C₁₋₄ loweralkyl diester represented by the formula (3).

The alcohol component as component b) for use in the esterificationincludes an aliphatic monohydric alcohol having 1 to 18 carbon atoms oran alicyclic monohydric alcohol having 3 to 10 carbon atoms, each havinga peroxide value of 1.0 meq/kg or less, and is represented by theformula R¹—OH or R²—OH wherein R and R² are as define above.

Especially,

-   -   1) when the alicyclic dicarboxylic acid represented by the        formula (2) or an acid anhydride thereof is used as the acid        component, it is preferable to use an aliphatic monohydric        alcohol having 1 to 18 carbon atoms or an alicyclic monohydric        alcohol having 3 to 10 carbon atoms, each having a peroxide        value of 1.0 meq/kg or less, and    -   2) when the alicyclic dicarboxylic acid di(C₁-C₄) lower alkyl        diester represented by the formula (3) is used as the acid        component, it is preferable to use an aliphatic monohydric        alcohol having 5 to 18 carbon atoms or an alicyclic monohydric        alcohol having 3 to 10 carbon atoms, each having a peroxide        value of 1.0 meq/kg or less.

The symbol A¹ in the invention represents a cyclohexane ring or acyclohexene ring. When A¹ is a cyclohexene ring, the position of doublebond may be any position relative to the ester groups, and is notlimited. X is a hydrogen atom or methyl. When X is methyl, thesubstitution position on the cyclohexane ring or cyclohexene ring ofmethyl is not limited. There is also no restriction on the substitutionpositions of two ester groups bonded to the cyclohexane ring orcyclohexene ring represented by A¹.

Among the diesters represented by the formula (1), preferred are thosewherein A¹ is a cyclohexane ring and X is hydrogen, those wherein A¹ isa cyclohexene ring and X is hydrogen, those wherein A¹ is a cyclohexenering and X is methyl. Further, while the positions of the two estergroups may be any of 1,2-positions, 1,3-positions and 1,4-positions ofcyclohexane ring or cyclohexene ring, 1,2-position is preferred in viewof hydrolysis stability of the diester of the formula (1).

Especially, cyclohexane-1,2-diesters, 3-cyclohexene-1,2-diesters,4-cyclohexene-1,2-diesters and the like are recommended.

In the present invention, R¹ and R² are the same or different and eachis a branched-chain alkyl group having 3 to 18 carbon atoms, astraight-chain alkyl group having 1 to 18 carbon atoms, a straight-chainalkenyl group having 2 to 18 carbon atoms or a cycloalkyl group having 3to 10 carbon atoms.

Examples of the branched-chain alkyl group having 3 to 18 carbon atomsare isopropyl, isobutyl, sec-butyl, isopentyl, isohexyl, 2-methylhexyl,2-methylheptyl, isoheptyl, 2-ethylhexyl, 2-octyl, isooctyl, isononyl,3,5,5-trimethylhexyl, 2,6-dimethyl-4-heptyl, isodecyl, isoundecyl,isododecyl, isotridecyl, isotetradecyl, isopentadecyl, isohexadecyl,isoheptadecyl, isooctadecyl, etc.

Examples of the straight-chain alkyl group having 1 to 18 carbon atomsare methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl,n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl,n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, etc.

Examples of the straight-chain alkenyl group having 2 to 18 carbon atomsare 2-hexenyl, 5-hexenyl, 2-heptenyl, 6-heptenyl, 2-octenyl, 8-nonenyl,2-decenyl, 2-undecenyl, 10-undecenyl, 11-dodecenyl, 12-tridecenyl,2-tetradecenyl, 2-pentadecenyl, 2-hexadecenyl, 15-hexadecenyl,2-heptadecenyl, 2-octadecenyl, 9-octadecenyl, etc.

Examples of the cycloalkyl group having 3 to 10 carbon atoms arecyclopentyl, cyclohexyl, methylcyclohexyl, dimethylcyclohexyl,cycloheptyl, cyclooctyl, etc.

Examples of the alicyclic dicarboxylic acid diester represented by theformula (1) obtained in the present invention are dimethyl1,2-cyclo-hexanedicarboxylate, diethyl 1,2-cyclohexanedicarboxylate,di(n-propyl) 1,2-cyclohexanedicarboxylate, di(n-butyl)1,2-cyclohexanedicarboxylate, di(n-pentyl) 1,2-cyclohexanedicarboxylate,di(n-hexyl) 1,2-cyclohexanedicarboxylate, di(n-heptyl)1,2-cyclohexanedicarboxylate, di(n-octyl) 1,2-cyclohexanedicarboxylate,di(n-nonyl) 1,2-cyclohexanedicarboxylate, di(n-decyl)1,2-cyclohexanedicarboxylate, di(n-undecyl)1,2-cyclohexanedicarboxylate, di(n-dodecyl)1,2-cyclohexanedicarboxylate, di(n-tridecyl)1,2-cyclohexanedicarboxylate, di(n-tetradecyl)1,2-cyclohexanedicarboxylate, di(n-pentadecyl)1,2-cyclohexanedicarboxylate, di(n-hexadecyl)1,2-cyclohexanedicarboxylate, di(n-octadecyl)1,2-cyclohexanedicarboxylate, dimethyl 4-cyclohexene-1,2-dicarboxylate,diethyl 4-cyclohexene-1,2-dicarboxylate,di(n-propyl)4-cyclohexene-1,2-dicarboxylate, di(n-butyl)4-cyclohexene-1,2-dicarboxylate, di(n-pentyl)4-cyclohexene-1,2-dicarboxylate,di(n-hexyl)4-cyclohexene-1,2-dicarboxylate,di(n-heptyl)4-cyclohexene-1,2-dicarboxylate,di(n-octyl)4-cyclohexene-1,2-dicarboxylate,di(n-nonyl)4-cyclohexene-1,2-dicarboxylate, di(n-decyl)4-cyclohexene-1,2-dicarboxylate,di(n-undecyl)4-cyclohexene-1,2-dicarboxylate,di(n-dodecyl)4-cyclohexene-1,2-dicarboxylate,di(n-tridecyl)4-cyclohexene-1,2-dicarboxylate,di(n-tetradecyl)4-cyclohexene-1,2-dicarboxylate, di(n-pentadecyl)4-cyclohexene-1,2-dicarboxylate,di(n-hexadecyl)4-cyclohexene-1,2-dicarboxylate,di(n-octadecyl)4-cyclohexene-1,2-dicarboxylate, dimethyl3-methyl-1,2-cyclohexanedicarboxylate, diethyl3-methyl-1,2-cyclohexanedicarboxylate,di(n-propyl)3-methyl-1,2-cyclohexanedicarboxylate,di(n-butyl)3-methyl-1,2-cyclohexanedicarboxylate,di(n-pentyl)3-methyl-1,2-cyclohexanedicarboxylate, di(n-hexyl)3-methyl-,2-cyclohexanedicarboxylate,di(n-heptyl)3-methyl-1,2-cyclohexanedicarboxylate,di(n-octyl)3-methyl-1,2-cyclohexanedicarboxylate,di(n-nonyl)3-methyl-1,2-cyclohexanedicarboxylate,di(n-decyl)3-methyl-1,2-cyclohexanedicarboxylate,di(n-undecyl)3-methyl-1,2-cyclohexanedicarboxylate,di(n-dodecyl)3-methyl-1,2-cyclohexanedicarboxylate,di(n-tridecyl)3-methyl-1,2-cyclohexanedicarboxylate,di(n-tetradecyl)3-methyl-1,2-cyclohexanedicarboxylate,di(n-pentadecyl)3-methyl-1,2-cyclohexanedicarboxylate,di(n-hexadecyl)3-methyl-1,2-cyclohexanedicarboxylate,di(n-octadecyl)3-methyl-1,2-cyclohexanedicarboxylate, dimethyl4-methyl-1,2-cyclohexanedicarboxylate, diethyl4-methyl-1,2-cyclohexanedicarboxylate,di(n-propyl)4-methyl-1,2-cyclohexanedicarboxylate,di(n-butyl)4-methyl-1,2-cyclohexanedicarboxylate,di(n-pentyl)4-methyl-1,2-cyclohexanedicarboxylate,di(n-hexyl)4-methyl-1,2-cyclohexanedicarboxylate,di(n-heptyl)4-methyl-1,2-cyclohexanedicarboxylate,di(n-octyl)4-methyl-1,2-cyclohexanedicarboxylate,di(n-nonyl)4-methyl-1,2-cyclohexanedicarboxylate,di(n-decyl)4-methyl-1,2-cyclohexanedicarboxylate,di(n-undecyl)4-methyl-1,2-cyclohexanedicarboxylate,di(n-dodecyl)4-methyl-1,2-cyclohexanedicarboxylate,di(n-tridecyl)4-methyl-1,2-cyclohexanedicarboxylate,di(n-tetradecyl)4-methyl-1,2-cyclohexanedicarboxylate,di(n-pentadecyl)4-methyl-1,2-cyclohexanedicarboxylate,di(n-hexadecyl)4-methyl-1,2-cyclohexanedicarboxylate,di(n-octadecyl)4-methyl-1,2-cyclohexanedicarboxylate, dimethyl3-methyl-4-cyclohexene-1,2-dicarboxylate, diethyl3-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-propyl)3-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-butyl)3-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-pentyl)3-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-hexyl)3-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-heptyl)3-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-octyl)3-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-nonyl)3-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-decyl)3-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-undecyl)3-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-dodecyl)3-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-tridecyl)3-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-tetradecyl)3-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-pentadecyl)3-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-hexadecyl)3-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-octadecyl)3-methyl-4-cyclohexene-1,2-dicarboxylate, dimethyl4-methyl-4-cyclohexene-1,2-dicarboxylate, diethyl4-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-propyl)4-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-butyl)4-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-pentyl)4-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-hexyl)4-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-heptyl)4-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-octyl)4-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-nonyl)4-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-decyl)4-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-undecyl)4-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-dodecyl)4-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-tridecyl)4-methyl-4-cyclohexene-1,2-dicarboxylate,di-(n-tetradecyl)4-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-pentadecyl)4-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-hexadecyl)4-methyl-4-cyclohexene-1,2-dicarboxylate,di(n-octadecyl)4-methyl-4-cyclohexene-1,2-dicarboxylate, diisopropyl1,2-cyclohexanedicarboxylate, diisobutyl 1,2-cyclohexanedicarboxylate,di(sec-butyl) 1,2-cyclohexanedicarboxylate, dicyclohexyl1,2-cyclohexanedicarboxylate, diisoheptyl 1,2-cyclohexanedicarboxylate,di(2-ethylhexyl) 1,2-cyclohexanedicarboxylate, diisononyl1,2-cyclohexanedicarboxylate, di(3,5,5-trimethylhexyl)1,2-cyclohexanedicarboxylate, di(2,6-dimethyl-4-heptyl)1,2-cyclohexanedicarboxylate, diisodecyl 1,2-cyclohexanedicarboxylate,diisoundecyl 1,2-cyclohexanedicarboxylate, diisotridecyl1,2-cyclohexanedicarboxylate, diisopentadecyl1,2-cyclohexanedicarboxylate, diisooctadecyl1,2-cyclohexanedicarboxylate, diisopropyl4-cyclohexene-1,2-dicarboxylate, diisobutyl4-cyclohexene-1,2-dicarboxylate,di(sec-butyl)4-cyclohexene-1,2-dicarboxylate, dicyclohexyl4-cyclohexene-1,2-dicarboxylate, diisoheptyl4-cyclohexene-1,2-dicarboxylate,di(2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate, diisononyl4-cyclohexene-1,2-dicarboxylate,di(3,5,5-trimethylhexyl)4-cyclohexene-1,2-dicarboxylate,di(2,6-dimethyl-4-heptyl)4-cyclohexene-1,2-dicarboxylate, diisodecyl4-cyclohexene-1,2-dicarboxylate, diisoundecyl4-cyclohexene-1,2-dicarboxylate, diisotridecyl4-cyclohexene-1,2-dicarboxylate, diisopentadecyl4-cyclohexene-1,2-dicarboxylate, diisooctadecyl4-cyclohexene-1,2-dicarboxylate, diisopropyl3-methyl-1,2-cyclohexanedicarboxylate, diisobutyl3-methyl-1,2-cyclohexanedicarboxylate,di(sec-butyl)3-methyl-1,2-cyclohexanedicarboxylate, dicyclohexyl3-methyl-1,2-cyclohexanedicarboxylate, diisoheptyl3-methyl-1,2-cyclohexanedicarboxylate,di(2-ethylhexyl)3-methyl-1,2-cyclohexanedicarboxylate, diisononyl3-methyl-1,2-cyclohexanedicarboxylate,di(3,5,5-trimethylhexyl)3-methyl-1,2-cyclohexanedicarboxylate,di(2,6-dimethyl-4-heptyl) 3-methyl-1,2-cyclohexanedicarboxylate,diisodecyl 3-methyl-1,2-cyclohexanedicarboxylate, diisoundecyl3-methyl-1,2-cyclohexanedicarboxylate, diisotridecyl3-methyl-1,2-cyclohexanedicarboxylate, diisopentadecyl3-methyl-1,2-cyclohexanedicarboxylate, diisooctadecyl3-methyl-1,2-cyclohexanedicarboxylate, diisopropyl4-methyl-1,2-cyclohexanedicarboxylate, diisobutyl4-methyl-1,2-cyclohexanedicarboxylate,di(sec-butyl)4-methyl-1,2-cyclohexanedicarboxylate, dicyclohexyl4-methyl-1,2-cyclohexanedicarboxylate, diisoheptyl4-methyl-1,2-cyclohexanedicarboxylate,di(2-ethylhexyl)4-methyl-1,2-cyclohexanedicarboxylate, diisononyl4-methyl-1,2-cyclohexanedicarboxylate, di(3,5,5-trimethylhexyl)4-methyl-1,2-cyclohexanedicarboxylate,di(2,6-dimethyl-4-heptyl)4-methyl-1,2-cyclohexanedicarboxylate,diisodecyl 4-methyl-1,2-cyclohexanedicarboxylate, diisoundecyl4-methyl-1,2-cyclohexanedicarboxylate, diisotridecyl4-methyl-1,2-cyclohexanedicarboxylate, diisopentadecyl4-methyl-1,2-cyclohexanedicarboxylate, diisooctadecyl4-methyl-1,2-cyclohexanedicarboxylate, diisopropyl3-methyl-4-cyclohexene-1,2-dicarboxylate, diisobutyl3-methyl-4-cyclohexene-1,2-dicarboxylate,di(sec-butyl)3-methyl-4-cyclohexene-1,2-dicarboxylate, dicyclohexyl3-methyl-4-cyclohexene-1,2-dicarboxylate, diisoheptyl3-methyl-4-cyclohexene-1,2-dicarboxylate,di(2-ethylhexyl)3-methyl-4-cyclohexene-1,2-dicarboxylate, diisononyl3-methyl-4-cyclohexene-1,2-dicarboxylate, di(3,5,5-trimethylhexyl)3-methyl-4-cyclohexene-1,2-dicarboxylate,di(2,6-dimethyl-4-heptyl)3-methyl-4-cyclohexene-1,2-dicarboxylate,diisodecyl 3-methyl-4-cyclohexene-1,2-dicarboxylate, diisoundecyl3-methyl-4-cyclohexene-1,2-dicarboxylate, diisotridecyl3-methyl-4-cyclohexene-1,2-dicarboxylate, diisopentadecyl3-methyl-4-cyclohexene-1,2-dicarboxylate, diisooctadecyl3-methyl-4-cyclohexene-1,2-dicarboxylate, diisopropyl4-methyl-4-cyclohexene-1,2-dicarboxylate, diisobutyl4-methyl-4-cyclohexene-1,2-dicarboxylate,di(sec-butyl)4-methyl-4-cyclohexene-1,2-dicarboxylate, dicyclohexyl4-methyl-4-cyclohexene-1,2-dicarboxylate, diisoheptyl4-methyl-4-cyclohexene-1,2-dicarboxylate,di(2-ethylhexyl)4-methyl-4-cyclohexene-1,2-dicarboxylate, diisononyl4-methyl-4-cyclohexene-1,2-dicarboxylate,di(3,5,5-trimethylhexyl)4-methyl-4-cyclohexene-1,2-dicarboxylate,di(2,6-dimethyl-4-heptyl)4-methyl-4-cyclohexene-1,2-dicarboxylate,diisodecyl 4-methyl-4-cyclohexene-1,2-dicarboxylate, diisoundecyl4-methyl-4-cyclohexene-1,2-dicarboxylate, diisotridecyl4-methyl-4-cyclohexene-1,2-dicarboxylate, diisopentadecyl4-methyl-4-cyclohexene-1,2-dicarboxylate, diisooctadecyl4-methyl-4-cyclohexene-1,2-dicarboxylate, etc.

Among the alicyclic dicarboxylic acid diesters represented by theformula (1), particularly preferred are those wherein R¹ and R² eachrepresents a straight-chain or branched-chain alkyl group having 3 to 11carbon atoms and A¹ represents a cyclohexane ring or a cyclohexene ring,and X is a hydrogen atom.

Preferred alicyclic dicarboxylic acid diesters include di(n-propyl)1,2-cyclohexane-dicarboxylate, di(n-butyl) 1,2-cyclohexanedicarboxylate,di(n-pentyl) 1,2-cyclohexanedicarboxylate, di(n-hexyl)1,2-cyclohexanedicarboxylate, di(n-heptyl) 1,2-cyclohexanedicarboxylate,di(n-octyl) 1,2-cyclohexanedicarboxylate, di(n-nonyl)1,2-cyclohexanedicarboxylate, di(n-decyl) 1,2-cyclohexanedicarboxylate,di(n-undecyl) 1,2-cyclohexanedicarboxylate, diisopropyl1,2-cyclohexanedicarboxylate, diisobutyl 1,2-cyclohexanedicarboxylate,di(sec-butyl) 1,2-cyclohexanedicarboxylate, dicyclohexyl1,2-cyclohexanedicarboxylate, diisoheptyl 1,2-cyclohexanedicarboxylate,di(2-ethlyhexyl) 1,2-cyclohexanedicarboxylate, diisononyl1,2-cyclohexanedicarboxylate, di(3,5,5-trimethylhexyl)1,2-cyclohexanedicarboxylate, di(2,6-dimethyl-4-heptyl)1,2-cyclohexanedicarboxylate, diisodecyl 1,2-cyclohexanedicarboxylate,diisoundecyl 1,2-cyclohexanedicarboxylate, di(n-propyl)4-cyclohexene-1,2-dicarboxylate,di(n-butyl)4-cyclohexene-1,2-dicarboxylate,di(n-pentyl)4-cyclohexene-1,2-dicarboxylate,di(n-hexyl)4-cyclohexene-1,2-dicarboxylate,di(n-heptyl)4-cyclohexene-1,2-dicarboxylate, di(n-octyl)4-cyclohexene-1,2-dicarboxylate,di(n-nonyl)4-cyclohexene-1,2-dicarboxylate,di(n-decyl)4-cyclohexene-1,2-dicarboxylate,di(n-undecyl)4-cyclohexene-1,2-dicarboxylate, diisopropyl4-cyclohexene-1,2-dicarboxylate, diisobutyl4-cyclohexene-1,2-dicarboxylate, di(sec-butyl)4-cyclohexene-1,2-dicarboxylate, dicyclohexyl4-cyclohexene-1,2-dicarboxylate, diisoheptyl4-cyclohexene-1,2-dicarboxylate,di(2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate, diisononyl4-cyclohexene-1,2-dicarboxylate,di(3,5,5-trimethylhexyl)4-cyclohexene-1,2-dicarboxylate,di(2,6-dimethyl-4-heptyl)4-cyclohexene-1,2-dicarboxylate, diisodecyl4-cyclohexene-1,2-dicarboxylate, diisoundecyl4-cyclohexene-1,2-dicarboxylate, etc.

The alicyclic dicarboxylic acid diesters represented by the formula (1)may include position isomers ascribed to ester groups. For example,4-cyclohexene-1,2-dicarboxylic acid diester may be an isomer dependingon whether two ester groups are present in equatorial or axialpositions. Specifically, the diester is a cis isomer when one of its twoester groups is in the equatorial position and the other is present inthe axial position. The diester is a trans isomer when both of its twoester groups are present in the equatorial position or in the axialposition. Both isomers can be used for use in a refrigerator oil.

When esterification temperature is set to higher than 210° C. and up toabout 230° C. in the preparation of the alicyclic dicarboxylic aciddiester, the esterification tends to predominantly give a trans isomer,whereas when esterification temperature is set at about 100 to about210° C., the esterification tends to predominantly give a cis isomer.

A cis-form ester can be isomerized to a trans-form ester. Isomerizationcan be performed according to the method disclosed, for example, in U.S.Pat. No. 5,231,218.

Process for Preparing an Ester of Embodiment I

In esterification of the alicyclic dicarboxylic acid of the formula (2)as component a) in item 1 and in ester interchange reaction of thealicyclic dicarboxylic acid diester of the formula (3) as component a′)in item 1, the same alcohol component is used as component b), b′) underthe same reaction conditions. In the following description, therefore,the esterification and the ester interchange reaction are collectivelyreferred to as “esterification” and the reaction conditions thereof aredescribed.

Alicyclic Dicarboxylic Acid of the Formula (2)

Examples of the alicyclic dicarboxylic acid of the formula (2) arecyclohexanedicarboxylic acid, cyclohexenedicarboxylic acid,methyl-substituted cyclohexanedicarboxylic acid and methyl-substitutedcyclohexenedicarboxylic acid. Further, anhydrides thereof can be alsoused, and two or more species of such compounds can be used as mixed.The substitution positions of its carboxyl groups may be any positionson the cyclohexane ring or cyclohexene ring without specific limitation.The position of the double bond in cyclohexenedicarboxylic acid may beany position relative to the carboxyl groups without specificlimitation.

However, with a view to prepare a diester of the formula (1) excellentin hydrolysis stability, it is preferable that the dicarboxylic acid isone having carboxyl groups in 1,2-positions of the cyclohexane orcyclohexene ring. In the case of cyclohexene ring, preferably the doublebond exists between the 4-position and 5-position relative to thecarboxyl groups at 1,2-positions.

More specific examples of the alicyclic dicarboxylic acid of the formula(2) are 1,2-cyclohexanedicarboxylic acid, 4-cyclohexene-1,2-dicarboxylicacid, 1-cyclohexene-1,2-dicarboxylic acid, 1,3-cyclohexanedicarboxylicacid, 1,4-cyclohexanedicarboxylic acid,3-methyl-1,2-cyclohexanedicarboxylic acid,4-methyl-1,2-cyclohexanedicarboxylic acid,3-methyl-4-cyclohexene-1,2-dicarboxylic acid and4-methyl-4-cyclohexene-1,2-dicarboxylic acid, and the anhydrides thereofare also usable.

Of these, 1,2-cyclohexanedicarboxylic acid,4-cyclohexene-1,2-dicarboxylic acid, 1-cyclohexene-1,2-dicarboxylicacid, 3-methyl-1,2-cyclohexanedicarboxylic acid,4-methyl-1,2-cyclohexanedicarboxylic acid,3-methyl-4-cyclohexene-1,2-dicarboxylic acid and4-methyl-4-cyclohexene-1,2-dicarboxylic acid are preferably recommended.

It is recommended that the alicyclic dicarboxylic acid of the formula(2) and its anhydride preferably have a peroxide value of 1.0 meq/kg orless. However, the alicyclic dicarboxylic acids are usually solid atroom temperature, and therefore increase in peroxide value thereof isrelatively small and would affect the performance of the present esterto a lesser degree, when used as a refrigerator lubricating oil,compared with increase in peroxide value of the alcohol of component b)used in the present invention.

The alicyclic dicarboxylic acids of the formula (2) and anhydridesthereof are known or can be prepared by known processes.

Alicyclic Dicarboxylic Acid Diester Represented by the Formula (3)

In the alicyclic dicarboxylic acid diester of the formula (3), R³ and R⁴are the same or different and each is a branched-chain alkyl grouphaving 3 or 4 carbon atoms or a straight-chain alkyl group having 1 to 4carbon atoms.

Specific examples of the alicyclic dicarboxylic acid diester of theformula (3) are dimethyl 1,2-cyclohexanedicarboxylate, diethyl1,2-cyclohexanedicarboxylate, di(n-propyl) 1,2-cyclohexanedicarboxylate,di(n-butyl) 1,2-cyclohexanedicarboxylate, diisobutyl1,2-cyclohexanedicarboxylate, diisopropyl 1,2-cyclohexanedicarboxylate,etc.

The alicyclic dicarboxylic acid diester of the formula (3) can beproduced by the process for preparing an alicyclic dicarboxylic aciddiester according to the invention. The lower alcohol of 1 to 4 carbonatoms to be used as the raw material is preferably one having a peroxidevalue of 1.0 meq/kg or less. Furthermore, the alicyclic dicarboxylicacid diesters of the formula (3) preferably have a peroxide value of 1.0meq/kg or less.

The alicyclic dicarboxylic acid diesters of the formula (3) are known orcan be easily prepared by known processes.

Component b) (Aliphatic Monohydric Alcohol)

As the aliphatic monohydric alcohol of 1 to 18 carbon atoms or thealicyclic monohydric alcohol of 3 to 10 carbon atoms to be used ascomponent b) in this esterification, recommended is, more specifically,a monohydric alcohol comprising a branched-chain alkyl group having 3 to18 carbon atoms, preferably 3 to 11 carbon atoms, a straight-chain alkylgroup having 1 to 18 carbon atoms, preferably 3 to 11 carbon atoms, astraight-chain alkenyl group having 2 to 18 carbon atoms or a cycloalkylgroup having 3 to 10 carbon atoms, and a hydroxyl group, the alcoholhaving a peroxide value of 1.0 meq/kg or less, preferably 0.5 meq/kg orless.

It is recommended in the ester interchange reaction to use as componentb) an aliphatic monohydric alcohol having 5 to 18 carbon atoms(especially, one made of a branched-chain alkyl group having 5 to 18carbon atoms or a straight-chain alkyl group having 5 to 18 carbon atomsand a hydroxyl group). More desirably usable is an aliphatic monohydricalcohol having 5 to 11 carbon atoms (especially, one made of abranched-chain alkyl group having 5 to 11 carbon atoms, a straight-chainalkyl group having 5 to 11 carbon atoms and a hydroxyl group).

As the alcohols of component b) used in the esterification reaction andalso of component b′) used in the ester interchange reaction,recommended are those having a carbonyl value of preferably 15 or less,more preferably 5 or less, and most preferably 1 or less.

When the contemplated ester of the formula (1) is prepared using analcohol having a peroxide value of 1.0 meq/kg or less and a carbonylvalue of 5 or less, the obtained ester shows well balanced propertieswhen used as a refrigerator oil. When the contemplated ester of theformula (1) is prepared using an alcohol having a peroxide value of 1.0meq/kg or less and a carbonyl value of 1 or less, the obtained estershows very well balanced properties when used as a refrigerator oil.

The term “peroxide value” used herein is described in 2.5.2-1996 ofStandard Methods for the Analysis of Fats, Oil and Related Materials(Japan Oil Chemists' Society), and refers to an amount of iodinereleased by addition of potassium iodide to a sample and expressed inmilliequivalent per kilogram of the sample, according to the methoddescribed therein.

The term “carbonyl value” used herein is described in 2.5.4-1996 ofStandard Methods for the Analysis of Fats, Oil and Related Materials(Japan Oil Chemists' Society), and refers to a value obtained by causing2,4-dinitrophenylhydrazine to act on a sample and converting the valueof its absorbance at 440 nm to a value per gram of the sample, accordingto the method described therein.

When an alcohol having a peroxide value of more than 1.0 meq/kg is used,the obtained alicyclic dicarboxylic acid diester is adversely affectedin the properties such as hue and peroxide value and involve problems inthe properties such as electrical insulating property, heat stabilityand hydrolysis stability.

An alcohol having a peroxide value of 1.0 meq/kg or less can be preparedby purifying an alcohol having a peroxide value of more than 1.0 meq/kgthrough distillation or through a treatment with a reducing agent tothereby decrease the peroxide value.

Generally an alcohol immediately after distillation has a peroxide valueof 1.0 meq/kg or less. However, such alcohol may show a peroxide valueof more than 1.0 meq/kg due to oxidation during a long-term storage(e.g. storage for 6 months or longer) depending on the storageconditions. Therefore, it is necessary to confirm a peroxide value ofthe alcohol before esterification.

The purification by distillation can be performed, e.g. by distilling analcohol having a peroxide value exceeding 1.0 meq/kg at 50-300° C. inthe presence of an alkali compound under reduced pressure. Useful alkalicompounds include, for example, NaOH, KOH, LiOH, etc. It isrecommendable to use the alkali compound in an amount of 0.001 to 0.5wt. % based on the alcohol.

The purification by reduction can be conducted, e.g. by stirring analcohol having a peroxide value exceeding 1.0 meq/kg at 30-150° C. inthe presence of a reducing agent for 30 minutes to 5 hours, preferably 1to 2 hours. Useful reducing agents include, for example, sodiumborohydride, potassium borohydride, lithium borohydride, lithiumaluminum hydride, etc. It is recommendable to use the reducing agent inan amount of 30 to 10,000 ppm based on the alcohol.

When an alicyclic dicarboxylic acid diester is prepared using an alcoholhaving a carbonyl value of 15 or less, preferably 5 or less, morepreferably 1 or less, the obtained ester has excellent hue and reducedperoxide value.

In the case of an alcohol having a carbonyl value of more than 15 aswell, its carbonyl value can be decreased to 15 or less by purificationthrough distillation or by purification through reduction, which may becarried out following the procedure of the foregoing method for loweringthe peroxide value.

Specific examples of the aliphatic monohydric alcohol to be used ascomponent b) in esterification are branched-chain alcohols of 3 to 18carbon atoms and straight-chain alcohols of 1 to 18 carbon atoms.Examples of the alicyclic monohydric alcohol include cycloalcohol of 3to 10 carbon atoms.

Especially,

-   -   1) when the alicyclic dicarboxylic acid represented by the        formula (2) or an anhydride thereof is used as the acid        component, it is preferable to use an aliphatic monohydric        alcohol having 1 to 18 carbon atoms or an alicyclic monohydric        alcohol having 3 to 10 carbon atoms, each having a peroxide        value of 1.0 meq/kg or less, and    -   2) when the alicyclic dicarboxylic acid di(C₁-C₄) lower alkyl        diester represented by the formula (3) is used as the acid        component, it is preferable to use an aliphatic monohydric        alcohol having 5 to 18 carbon atoms or an alicyclic monohydric        alcohol having 3 to 10 carbon atoms, each having a peroxide        value of 1.0 meq/kg or less.

More specific examples of the aliphatic monohydric branched-chainalcohol are isopropanol, isobutanol, sec-butanol, isopentanol,isohexanol, 2-methylhexanol, 1-methylheptanol, 2-methylheptanol,isoheptanol, 2-ethylhexanol, 2-octanol, isooctanol, isononanol,3,5,5-trimethylhexanol, 2,6-dimethyl-4-heptanol, isodecanol,isoundecanol, isododecanol, isotridecanol, isotetradecanol,isopentadecanol, isohexadecanol, isoheptadecanol, isooctadecanol, etc.

More specific examples of the aliphatic monohydric straight-chainalcohol are methanol, ethanol, n-propanol, n-butanol, n-pentanol,n-hexanol, n-heptanol, n-octanol, n-nonanol, n-decanol, n-undecanol,n-dodecanol, n-tridecanol, n-tetradecanol, n-pentadecanol,n-hexadecanol, n-heptadecanol, n-octadecanol, 2-hexenol, 5-hexenol,2-heptenol, 6-heptenol, 2-octenol, 8-nonenol, 2-decenol, 2-undecenol,10-undecenol, 11-dodecenol, 12-tridecenol, 2-tetradecenol,2-pentadecenol, 2-hexadecenol, 15-hexadecenol, 2-heptadecenol,2-octadecenol, 9-octadecenol, etc.

More specific examples of the alicyclic monohydric cycloalcohol includecyclohexanol, methylcyclohexanol, dimethylcyclohexanol, etc.

Among the foregoing alcohols, saturated alcohols of 1 to 18 carbon atomsare preferable to achieve good heat stability. Alcohols of 1 to 11carbon atoms are desirable to achieve better miscibility with arefrigerant.

The above alcohols can be esterified alone as an alcohol component, ortwo or more species of alcohol can be used as mixed.

When a mixture of two or more species of the alcohol is used foresterification, the obtained alicyclic dicarboxylic acid diester of theformula (1) is a mixed diester wherein R¹ and R² are different. Suchmixed diester is suitably used as well.

In esterification, the alcohol component is used in an amount of about 1to about 1.5 equivalents, preferably about 1.05 to about 1.2equivalents, per equivalent of carboxylic acid group of component a),i.e., an alicyclic dicarboxylic acid of the formula (2) or an anhydridethereof or an alicyclic dicarboxylic acid diester of the formula (3).

It is preferred that neither the acid component nor the alcoholcomponent to be used in esterification contain a sulfur element or aphosphorus element as impurities.

Catalyst

In the present invention, the esterification reaction is carried out inthe absence of a catalyst or in the presence of a sulfur-free andphosphorus-free catalyst. It is particularly recommended to carry outthe esterification in the presence of a sulfur-free and phosphorus-freecatalyst.

The sulfur-free and phosphorus-free catalyst for use in theesterification of the invention is a catalyst which does not contain asulfur element or a phosphorus element in the constituent elements ofthe catalyst. Specifically, examples of useful catalysts are Lewis acidsand alkali metal compounds which contain neither a sulfur element nor aphosphorus element. More specifically, examples of Lewis acids arealuminum derivatives, tin derivatives, titanium derivatives, leadderivatives and zinc derivatives. Examples of alkali metal compounds aresodium alkoxide, potassium alkoxide, sodium hydroxide, potassiumhydroxide, etc. These catalysts can be used either alone or incombination. Preferred catalysts are those containing no sulfur elementor phosphorus element as impurities.

Of such catalysts, particularly preferred are tetra(C₃-C₈ alkyl)titanate, titanium oxide, titanium hydroxide, sodium alkoxide of 1 to 4carbon atoms, sodium hydroxide, C₃-C₁₂ fatty acid tin salt, tin oxide,tin hydroxide, zinc oxide, zinc hydroxide, lead oxide, lead hydroxide,aluminum oxide and aluminum hydroxide. The amount of the catalyst to beused is, for example, about 0.05 to about 1 wt. % based on the totalamount of the acid component (component a) above) and the alcoholcomponent (component b) above) used as the raw materials for synthesisof the ester.

Reaction Conditions

The esterification temperature is, for example, in the range of 100 to230° C. Usually the reaction is completed in 3 to 30 hours.

To accelerate the distillation of water formed by the reaction, awater-entraining agent such as benzene, toluene, xylene, cyclohexane orthe like may be used in the esterification.

The esterification reaction may be carried out under atmosphericpressure or under reduced pressure (e.g., 133 to 66500 Pa). However,from a viewpoint of accelerating the esterification reaction, it ispreferable to combine esterification reaction under atmospheric pressureand esterification reaction under reduced pressure. Particularly, it isrecommended to carry out the esterification reaction under reducedpressure in a later stage of the reaction (such as the stage in whichthe total acid number of the reaction mixture becomes about 10 mgKOH/gor less) when the esterification reaction velocity becomes low.

When oxides, peroxides, carbonyl compounds and like oxygen-containingorganic compound are produced in esterification reaction due tooxidative deterioration of the raw material, the obtained ester and theorganic solvent (water-entraining agent), the hygroscopicity, hydrolysisstability and electrical insulating property would be adverselyaffected. Consequently, the esterification reaction is preferablycarried out in an atmosphere or stream of inert gas such as nitrogengas.

In the process of the invention for preparing an alicyclic dicarboxylicacid diester for use as a lubricating oil for refrigerators, apreferable combinations of properties of the aliphatic monohydricalcohol of 1 to 18 carbon atoms or alicyclic monohydric alcohol of 3 to10 carbon atoms constituting the ester are, for example, as follows:

-   -   1) an aliphatic monohydric alcohol having a peroxide value of        1.0 meq/kg or less,    -   2) an aliphatic monohydric alcohol having a peroxide value of        1.0 meq/kg or less and a carbonyl value of 15 or less,    -   3) an aliphatic monohydric alcohol having a peroxide value of        1.0 meq/kg or less and a carbonyl value of 5 or less,    -   4) an aliphatic monohydric alcohol having a peroxide value of        0.5 meq/kg or less and a carbonyl value of 5 or less, and    -   5) an aliphatic monohydric alcohol having a peroxide value of        0.5 meq/kg or less and a carbonyl value of 1 or less.

Esters of Embodiment II and Process for Preparation Thereof

Alicyclic or Aromatic Adjacent Dicarboxylic Acid Mixed Diester Usefulfor a Refrigerator Oil

According to the present invention, by carrying out two-stepesterification comprising the steps of(a) reacting an alicyclic or aromatic adjacent dicarboxylic anhydriderepresented by the formula (5s)

wherein A and X are as defined above, with “alcohol component 1” to bedescribed later to produce an alicyclic or aromatic adjacentdicarboxylic acid monoester represented by the formula (5)

wherein A represents a cyclohexane ring, a cyclohexene ring or a benzenering, X is a hydrogen atom or methyl group, and R⁵ is a branched-chainalkyl group having 3 to 18 carbon atoms, a straight-chain alkyl grouphaving 1 to 18 carbon atoms, a straight-chain alkenyl group having 2 to18 carbon atoms or a cycloalkyl group having 3 to 10 carbon atoms andthe groups —COOR⁵ and —COOH are attached to two adjacent carbon atoms ofthe cyclohexane, cyclohexene or benzene ring represented by A (“step(a)” or first stage), and(b) esterifying the alicyclic or aromatic adjacent dicarboxylic acidmonoester of the formula (5) with “alcohol component 2” (“step (b)” orsecond stage), the foregoing alicyclic or aromatic adjacent dicarboxylicacid mixed diester represented by the formula (4)

wherein A and X are as defined above, R⁵ and R⁶ are different from eachother and each is a branched-chain alkyl group having 3 to 18 carbonatoms, a straight-chain alkyl group having 1 to 18 carbon atoms, astraight-chain alkenyl group having 2 to 18 carbon atoms or a cycloalkylgroup having 3 to 10 carbon atoms, and the groups —COOR⁵ and —COOR⁶ areattached to two adjacent carbon atoms of the cyclohexane, cyclohexene orbenzene ring represented by A is obtained, and this mixed diester isused as a refrigerator oil, wherein

-   -   said “alcohol component 1” comprises a monohydric alcohol of 1        to 5 carbon atoms (P) and optionally a monohydric alcohol of 6        to 18 carbon atoms (Q) (wherein (P):(Q)=0.1:99.9 to 100:0 (molar        ratio)), and    -   said “alcohol component 2” comprises a monohydric alcohol of 6        to 18 carbon atoms (T) and optionally a monohydric alcohol of 1        to 5 carbon atoms (S) (wherein (S):(T)=0:100 to 99.9:0.1 (molar        ratio)).

The monohydric alcohol of 1 to 5 carbon atoms (P) constituting said“alcohol component 1” is, more specifically, an alcohol composed of abranched-chain alkyl group having 3 to 5 carbon atoms, a straight-chainalkyl group having 1 to 5 carbon atoms, a straight-chain alkenyl grouphaving 2 to 5 carbon atoms or a cycloalkyl group having 3 to 5 carbonatoms, and a hydroxyl group. The monohydric alcohol of 6 to 18 carbonatoms (Q) is an alcohol composed of a branched-chain alkyl group having6 to 18 carbon atoms, a straight-chain alkyl group having 6 to 18 carbonatoms, a straight-chain alkenyl group having 6 to 18 carbon atoms or acycloalkyl group having 6 to 10 carbon atoms, and a hydroxyl group.

Preferably, said alcohol component 1 is an alcohol selected frommonohydric alcohols (P) of 1 to 5 carbon atoms.

The monohydric alcohol of 1 to 5 carbon atoms (S) constituting said“alcohol component 2” is, more specifically, an alcohol composed of abranched-chain alkyl group having 3 to 5 carbon atoms, a straight-chainalkyl group having 1 to 5 carbon atoms, a straight-chain alkenyl grouphaving 2 to 5 carbon atoms or a cycloalkyl group having 3 to 5 carbonatoms, and a hydroxyl group. The monohydric alcohol of 6 to 18 carbonatoms (T) is an alcohol composed of a branched-chain alkyl group having6 to 18 carbon atoms, a straight-chain alkyl group having 6 to 18 carbonatoms, a straight-chain alkenyl group having 6 to 18 carbon atoms or acycloalkyl group having 6 to 10 carbon atoms, and a hydroxyl group.

Preferably the alcohol component 2 is an alcohol selected from themonohydric alcohols (T) of 6 to 18 carbon atoms.

In the alicyclic or aromatic adjacent dicarboxylic acid mixed diester ofthe invention represented by the formula (4), R⁵ and R⁶ are differentfrom each other.

When, for example, an alcohol (R⁵OH) selected from the monohydricalcohols of 1 to 5 carbon atoms (P) is used as alcohol component 1, andan alcohol (R⁶OH) selected from the monohydric alcohols (T) of 6 to 18carbon atoms is used as alcohol component 2, in the resulting alicyclicor aromatic adjacent dicarboxylic acid mixed diester of the inventionrepresented by the formula (4), R⁵ is a group resulting from eliminationof the hydroxyl group from said monohydric alcohol of 1 to 5 carbonatoms (S), i.e. a branched-chain alkyl group having 3 to 5 carbon atoms,a straight-chain alkyl group having 1 to 5 carbon atoms, astraight-chain alkenyl group having 2 to 5 carbon atoms or a cycloalkylgroup having 3 to 5 carbon atoms, and R⁶ is a group resulting fromelimination of the hydroxyl group from the monohydric alcohols of 6 to18 carbon atoms (T), i.e. a branched-chain alkyl group having 6 to 18carbon atoms, a straight-chain alkyl group having 6 to 18 carbon atoms,a straight-chain alkenyl group having 6 to 18 carbon atoms or acycloalkyl group having 6 to 10 carbon atoms.

In the present invention, A represents a cyclohexane ring, a cyclohexenering or a benzene ring, X is a hydrogen atom or methyl, R⁵ and R⁶ aredifferent from each other and each is a branched-chain alkyl grouphaving 3 to 18 carbon atoms, a straight-chain alkyl group having 1 to 18carbon atoms, a straight-chain alkenyl group having 2 to 0.18 carbonatoms or a cycloalkyl group having 3 to 10 carbon atoms.

The group —COOR⁵ is present in a position adjacent to the substitutionposition of the group —COOR⁶ on the cyclohexane ring, cyclohexene ringor benzene ring represented by A.

Further, in the cyclohexane ring or in the cyclohexene ring, when thegroup —COOR⁵ is present in the 1-position, the group —COOR⁶ is presentin the 2-position, and when the group —COOR⁵ is present in the2-position, the group —COOR⁶ is present in the 1-position.

Specific examples of the alicyclic dicarboxylic acid mixed diesterrepresented by the formula (4) are (methyl)(cyclohexyl)1,2-cyclohexanedicarboxylate, (methyl) (n-heptyl)1,2-cyclohexanedicarboxylate, (methyl)(isoheptyl)1,2-cyclohexanedicarboxylate, (methyl)(n-octyl)1,2-cyclohexanedicarboxylate, (methyl)(2-ethylhexyl)1,2-cyclohexanedicarboxylate, (methyl) (isooctyl)1,2-cyclohexanedicarboxylate, (methyl)(2-octyl)1,2-cyclohexanedicarboxylate, (methyl)(n-nonyl)1,2-cyclohexanedicarboxylate, (methyl)(isononyl)1,2-cyclohexanedicarboxylate, (methyl) (3,5,5-trimethylhexyl)1,2-cyclohexanedicarboxylate, (methyl)(n-decyl)1,2-cyclohexanedicarboxylate, (methyl)(isodecyl)1,2-cyclohexanedicarboxylate, (methyl)(n-undecyl)1,2-cyclohexanedicarboxylate, (methyl)(isoundecyl)1,2-cyclohexanedicarboxylate, (methyl)(n-dodecyl)1,2-cyclohexanedicarboxylate, (methyl)(isododecyl)1,2-cyclohexanedicarboxylate, (methyl)(n-tridecyl)1,2-cyclohexanedicarboxylate, (methyl)(isotridecyl)1,2-cyclohexanedicarboxylate, (methyl)(n-tetradecyl)1,2-cyclohexanedicarboxylate, (methyl)(isotetradecyl)1,2-cyclohexanedicarboxylate, (methyl)(n-pentadecyl)1,2-cyclohexanedicarboxylate, (methyl)(isopentadecyl)1,2-cyclohexanedicarboxylate, (methyl)(n-hexadecyl)1,2-cyclohexanedicarboxylate, (methyl)(isohexadecyl)1,2-cyclohexanedicarboxylate, (methyl)(n-heptadecyl)1,2-cyclohexanedicarboxylate, (methyl)(isoheptadecyl)1,2-cyclohexanedicarboxylate, (methyl)(n-octadecyl)1,2-cyclohexanedicarboxylate, (methyl)(isooctadecyl)1,2-cyclohexanedicarboxylate, (ethyl)(cyclohexyl)1,2-cyclohexanedicarboxylate, (ethyl)(n-heptyl)1,2-cyclohexanedicarboxylate, (ethyl)(isoheptyl)1,2-cyclohexanedicarboxylate, (ethyl)(n-octyl)1,2-cyclohexanedicarboxylate, (ethyl)(2-ethylhexyl)1,2-cyclohexanedicarboxylate, (ethyl)(isooctyl)1,2-cyclohexanedicarboxylate, (ethyl)(2-octyl)1,2-cyclohexanedicarboxylate, (ethyl)(n-nonyl)1,2-cyclohexanedicarboxylate, (ethyl)(isononyl)1,2-cyclohexanedicarboxylate, (ethyl)(3,5,5-trimethylhexyl)1,2-cyclohexanedicarboxylate, (ethyl)(n-decyl)1,2-cyclohexanedicarboxylate, (ethyl)(isodecyl)1,2-cyclohexanedicarboxylate, (ethyl)(n-undecyl)1,2-cyclohexanedicarboxylate, (ethyl)(isoundecyl)1,2-cyclohexanedicarboxylate, (ethyl)(n-dodecyl)1,2-cyclohexanedicarboxylate, (ethyl)(isododecyl)1,2-cyclohexanedicarboxylate, (ethyl)(n-tridecyl)1,2-cyclohexanedicarboxylate, (ethyl)(isotridecyl)1,2-cyclohexanedicarboxylate, (ethyl)(n-tetradecyl)1,2-cyclohexanedicarboxylate, (ethyl)(isotetradecyl)1,2-cyclohexanedicarboxylate, (ethyl)(n-pentadecyl)1,2-cyclohexanedicarboxylate, (ethyl)(isopentadecyl)1,2-cyclohexanedicarboxylate, (ethyl)(n-hexadecyl)1,2-cyclohexanedicarboxylate, (ethyl)(isohexadecyl)1,2-cyclohexanedicarboxylate, (ethyl) (n-heptadecyl)1,2-cyclohexanedicarboxylate, (ethyl)(isoheptadecyl)1,2-cyclohexanedicarboxylate, (ethyl)(n-octadecyl)1,2-cyclohexanedicarboxylate, (ethyl)(isooctadecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(cyclohexyl)1,2-cyclohexanedicarboxylate, (n-propyl)(n-heptyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isoheptyl)1,2-cyclohexanedicarboxylate, (n-propyl)(n-octyl)1,2-cyclohexanedicarboxylate, (n-propyl)(2-ethylhexyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isooctyl)1,2-cyclohexanedicarboxylate, (n-propyl)(2-octyl)1,2-cyclohexanedicarboxylate, (n-propyl)(n-nonyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isononyl)1,2-cyclohexanedicarboxylate, (n-propyl)(3,5,5-trimethylhexyl)1,2-cyclohexanedicarboxylate, (n-propyl)(n-decyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isodecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(n-undecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isoundecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(n-dodecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isododecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(n-tridecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isotridecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(n-tetradecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isotetradecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(n-pentadecyl)1,2-cyclohexanedicarboxylate, (n-propyl) (isopentadecyl)1,2-cyclohexanedicarboxylate, (n-propyl) (n-hexadecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isohexadecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(n-heptadecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isoheptadecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(n-octadecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isooctadecyl)1,2-cyclohexanedicarboxylate, (isopropyl) (cyclohexyl)1,2-cyclohexanedicarboxylate, (isopropyl)(n-heptyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isoheptyl)1,2-cyclohexanedicarboxylate, (isopropyl)(n-octyl)1,2-cyclohexanedicarboxylate, (isopropyl)(2-ethylhexyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isooctyl)1,2-cyclohexanedicarboxylate, (isopropyl)(2-octyl)1,2-cyclohexanedicarboxylate, (isopropyl)(n-nonyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isononyl)1,2-cyclohexanedicarboxylate, (isopropyl)(3,5,5-trimethylhexyl)1,2-cyclohexanedicarboxylate, (isopropyl)(n-decyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isodecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(n-undecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isoundecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(n-dodecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isododecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(n-tridecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isotridecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(n-tetradecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isotetradecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(n-pentadecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isopentadecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(n-hexadecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isohexadecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(n-heptadecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isoheptadecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(n-octadecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isooctadecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(cyclohexyl)1,2-cyclohexanedicarboxylate, (n-butyl)(n-heptyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isoheptyl)1,2-cyclohexanedicarboxylate, (n-butyl)(n-octyl)1,2-cyclohexanedicarboxylate, (n-butyl)(2-ethylhexyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isooctyl)1,2-cyclohexanedicarboxylate, (n-butyl)(2-octyl)1,2-cyclohexanedicarboxylate, (n-butyl)(n-nonyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isononyl)1,2-cyclohexanedicarboxylate, (n-butyl)(3,5,5-trimethylhexyl)1,2-cyclohexanedicarboxylate, (n-butyl)(n-decyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isodecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(n-undecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isoundecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(n-dodecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isododecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(n-tridecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isotridecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(n-tetradecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isotetradecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(n-pentadecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isopentadecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(n-hexadecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isohexadecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(n-heptadecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isoheptadecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(n-octadecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isooctadecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(cyclohexyl)1,2-cyclohexanedicarboxylate, (isobutyl)(n-heptyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isoheptyl)1,2-cyclohexanedicarboxylate, (isobutyl) (n-octyl)1,2-cyclohexanedicarboxylate, (isobutyl)(2-ethylhexyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isooctyl)1,2-cyclohexanedicarboxylate, (isobutyl)(2-octyl)1,2-cyclohexanedicarboxylate, (isobutyl)(n-nonyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isononyl)1,2-cyclohexanedicarboxylate, (isobutyl)(3,5,5-trimethylhexyl)1,2-cyclohexanedicarboxylate, (isobutyl)(n-decyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isodecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(n-undecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isoundecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(n-dodecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isododecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(n-tridecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isotridecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(n-tetradecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isotetradecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(n-pentadecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isopentadecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(n-hexadecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isohexadecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(n-heptadecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isoheptadecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(n-octadecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isooctadecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(cyclohexyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(n-heptyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isoheptyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(n-octyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(2-ethylhexyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isooctyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(2-octyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(n-nonyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isononyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(3,5,5-trimethylhexyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(n-decyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isodecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(n-undecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isoundecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(n-dodecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isododecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(n-tridecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isotridecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(n-tetradecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isotetradecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(n-pentadecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isopentadecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(n-hexadecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isohexadecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(n-heptadecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isoheptadecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(n-octadecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isooctadecyl)1,2-cyclohexanedicarboxylate, (methyl)(cyclohexyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(n-heptyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(isoheptyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(n-octyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(isooctyl).4-cyclohexene-1,2-dicarboxylate, (methyl)(2-octyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(n-nonyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(isononyl)4-cyclohexene-1,2-dicarboxylate, (methyl) (3,5,5-trimethylhexyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(n-decyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(isodecyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(n-undecyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(isoundecyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(n-dodecyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(isododecyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(n-tridecyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(isotridecyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(n-tetradecyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(isotetradecyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(n-pentadecyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(isopentadecyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(n-hexadecyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(isohexadecyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(n-heptadecyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(isoheptadecyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(n-octadecyl)4-cyclohexene-1,2-dicarboxylate, (methyl)(isooctadecyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(cyclohexyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(n-heptyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(isoheptyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(n-octyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(isooctyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(2-octyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(n-nonyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(isononyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(3,5,5-trimethylhexyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(n-decyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(isodecyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(n-undecyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(isoundecyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(n-dodecyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(isododecyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(n-tridecyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(isotridecyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(n-tetradecyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(isotetradecyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(n-pentadecyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(isopentadecyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(n-hexadecyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(isohexadecyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(n-heptadecyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(isoheptadecyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(n-octadecyl)4-cyclohexene-1,2-dicarboxylate, (ethyl)(isooctadecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(cyclohexyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(n-heptyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isoheptyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(n-octyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isooctyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(2-octyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(n-nonyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isononyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(3,5,5-trimethylhexyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(n-decyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isodecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(n-undecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isoundecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(n-dodecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isododecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(n-tridecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isotridecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(n-tetradecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isotetradecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(n-pentadecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isopentadecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(n-hexadecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isohexadecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(n-heptadecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isoheptadecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(n-octadecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isooctadecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(cyclohexyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(n-heptyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isoheptyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(n-octyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isooctyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(2-octyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(n-nonyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isononyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(3,5,5-trimethylhexyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(n-decyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isodecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(n-undecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isoundecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(n-dodecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isododecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(n-tridecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isotridecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(n-tetradecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isotetradecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(n-pentadecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isopentadecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(n-hexadecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isohexadecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(n-heptadecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isoheptadecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(n-octadecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isooctadecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(cyclohexyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(n-heptyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isoheptyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(n-octyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isooctyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(2-octyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(n-nonyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isononyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl) (3,5,5-trimethylhexyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(n-decyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isodecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(n-undecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isoundecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(n-dodecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isododecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(n-tridecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isotridecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(n-tetradecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isotetradecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(n-pentadecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isopentadecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(n-hexadecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isohexadecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(n-heptadecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isoheptadecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(n-octadecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isooctadecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(cyclohexyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(n-heptyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isoheptyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(n-octyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isooctyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(2-octyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(n-nonyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isononyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(3,5,5-trimethylhexyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(n-decyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isodecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(n-undecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isoundecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(n-dodecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isododecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(n-tridecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isotridecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(n-tetradecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isotetradecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(n-pentadecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isopentadecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(n-hexadecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isohexadecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(n-heptadecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isoheptadecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(n-octadecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isooctadecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(cyclohexyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(n-heptyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isoheptyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(n-octyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isooctyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(2-octyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(n-nonyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isononyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(3,5,5-trimethylhexyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(n-decyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isodecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(n-undecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isoundecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(n-dodecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isododecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(n-tridecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isotridecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(n-tetradecyl)4-cyclohexene-1,2-dicarboxy late, (sec-butyl)(isotetradecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(n-pentadecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isopentadecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(n-hexadecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isohexadecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(n-heptadecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isoheptadecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(n-octadecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isooctadecyl)4-cyclohexene-1,2-dicarboxylate.

Recommendable are preferably (n-propyl) (cyclohexyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isoheptyl)1,2-cyclohexanedicarboxylate, (n-propyl)(2-ethylhexyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isooctyl)1,2-cyclohexanedicarboxylate, (n-propyl)(2-octyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isononyl)1,2-cyclohexanedicarboxylate, (n-propyl) (3,5,5-trimethylhexyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isodecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isoundecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isododecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isotridecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isotetradecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isopentadecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isohexadecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isoheptadecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(isooctadecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(cyclohexyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isoheptyl)1,2-cyclohexanedicarboxylate, (isopropyl)(2-ethylhexyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isooctyl)1,2-cyclohexanedicarboxylate, (isopropyl)(2-octyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isononyl)1,2-cyclohexanedicarboxylate, (isopropyl)(3,5,5-trimethylhexyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isodecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isoundecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isododecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isotridecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isotetradecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isopentadecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isohexadecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isoheptadecyl)1,2-cyclohexanedicarboxylate, (isopropyl)(isooctadecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(cyclohexyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isoheptyl)1,2-cyclohexanedicarboxylate, (n-butyl)(2-ethylhexyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isooctyl)1,2-cyclohexanedicarboxylate, (n-butyl)(2-octyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isononyl)1,2-cyclohexanedicarboxylate, (n-butyl)(3,5,5-trimethylhexyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isodecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isoundecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isododecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isotridecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isotetradecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isopentadecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isohexadecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isoheptadecyl)1,2-cyclohexanedicarboxylate, (n-butyl)(isooctadecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(cyclohexyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isoheptyl)1,2-cyclohexanedicarboxylate, (isobutyl)(2-ethylhexyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isooctyl)1,2-cyclohexanedicarboxylate, (isobutyl)(2-octyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isononyl)1,2-cyclohexanedicarboxylate, (isobutyl)(3,5,5-trimethylhexyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isodecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isoundecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isododecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isotridecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isotetradecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isopentadecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isohexadecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isoheptadecyl)1,2-cyclohexanedicarboxylate, (isobutyl)(isooctadecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(cyclohexyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isoheptyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(2-ethylhexyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isooctyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(2-octyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isononyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(3,5,5-trimethylhexyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isodecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isoundecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isododecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isotridecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isotetradecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isopentadecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isohexadecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isoheptadecyl)1,2-cyclohexanedicarboxylate, (sec-butyl)(isooctadecyl)1,2-cyclohexanedicarboxylate, (n-propyl)(cyclohexyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isoheptyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isooctyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(2-octyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isononyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(3,5,5-trimethylhexyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isodecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isoundecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isododecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isotridecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isotetradecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isopentadecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isohexadecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isoheptadecyl)4-cyclohexene-1,2-dicarboxylate, (n-propyl)(isooctadecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(cyclohexyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isoheptyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isooctyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(2-octyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isononyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(3,5,5-trimethylhexyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isodecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isoundecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isododecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isotridecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isotetradecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isopentadecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isohexadecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isoheptadecyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl)(isooctadecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(cyclohexyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isoheptyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isooctyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(2-octyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isononyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(3,5,5-trimethylhexyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isodecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isoundecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isododecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isotridecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isotetradecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isopentadecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isohexadecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isoheptadecyl)4-cyclohexene-1,2-dicarboxylate, (n-butyl)(isooctadecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(cyclohexyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isoheptyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isooctyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(2-octyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isononyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(3,5,5-trimethylhexyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isodecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isoundecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isododecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isotridecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isotetradecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isopentadecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isohexadecyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl)(isoheptadecyl)4-cyclohexene-0,1,2-dicarboxylate, (isobutyl)(isooctadecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(cyclohexyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isoheptyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isooctyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(2-octyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isononyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(3,5,5-trimethylhexyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isodecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isoundecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isododecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isotridecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isotetradecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isopentadecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isohexadecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isoheptadecyl)4-cyclohexene-1,2-dicarboxylate, (sec-butyl)(isooctadecyl)4-cyclohexene-1,2-dicarboxylate.

Specific examples of the aromatic adjacent dicarboxylic acid mixeddiester of the formula (4) are (methyl)(cyclohexyl) phthalate,(methyl)(n-heptyl) phthalate, (methyl)(isoheptyl) phthalate,(methyl)(n-octyl) phthalate, (methyl)(2-ethylhexyl) phthalate,(methyl)(isooctyl) phthalate, (methyl)(2-octyl) phthalate,(methyl)(n-nonyl) phthalate, (methyl)(isononyl) phthalate,(methyl)(3,5,5-trimethylhexyl) phthalate, (methyl)(n-decyl) phthalate,(methyl)(isodecyl) phthalate, (methyl)(n-undecyl) phthalate,(methyl)(isoundecyl) phthalate, (methyl)(n-dodecyl) phthalate,(methyl)(isododecyl) phthalate, (methyl)(n-tridecyl) phthalate, (methyl)(isotridecyl) phthalate, (methyl)(n-tetradecyl) phthalate,(methyl)(isotetradecyl) phthalate, (methyl)(n-pentadecyl) phthalate,(methyl)(isopentadecyl) phthalate, (methyl)(n-hexadecyl) phthalate,(methyl)(isohexadecyl) phthalate, (methyl)(n-heptadecyl) phthalate,(methyl)(isoheptadecyl) phthalate, (methyl)(n-octadecyl) phthalate,(methyl) (isooctadecyl) phthalate, (ethyl)(cyclohexyl) phthalate,(ethyl)(n-heptyl) phthalate, (ethyl)(isoheptyl) phthalate,(ethyl)(n-octyl) phthalate, (ethyl)(2-ethylhexyl) phthalate,(ethyl)(isooctyl) phthalate, (ethyl)(2-octyl) phthalate,(ethyl)(n-nonyl) phthalate, (ethyl)(isononyl) phthalate,(ethyl)(3,5,5-trimethylhexyl) phthalate, (ethyl)(n-decyl) phthalate,(ethyl)(isodecyl) phthalate, (ethyl)(n-undecyl) phthalate,(ethyl)(isoundecyl) phthalate, (ethyl)(n-dodecyl) phthalate,(ethyl)(isododecyl) phthalate, (ethyl)(n-tridecyl) phthalate,(ethyl)(isotridecyl) phthalate, (ethyl)(n-tetradecyl) phthalate,(ethyl)(isotetradecyl) phthalate, (ethyl)(n-pentadecyl) phthalate,(ethyl)(isopentadecyl) phthalate, (ethyl)(n-hexadecyl) phthalate,(ethyl)(isohexadecyl) phthalate, (ethyl)(n-heptadecyl) phthalate,(ethyl)(isoheptadecyl) phthalate, (ethyl)(n-octadecyl) phthalate,(ethyl)(isooctadecyl) phthalate, (n-propyl)(cyclohexyl) phthalate,(n-propyl)(n-heptyl) phthalate, (n-propyl) (isoheptyl) phthalate,(n-propyl)(n-octyl) phthalate, (n-propyl)(2-ethylhexyl) phthalate,(n-propyl) (isooctyl) phthalate, (n-propyl)(2-octyl) phthalate,(n-propyl) (n-nonyl) phthalate, (n-propyl)(isononyl) phthalate,(n-propyl)(3,5,5-trimethylhexyl) phthalate, (n-propyl) (n-decyl)phthalate, (n-propyl)(isodecyl) phthalate, (n-propyl)(n-undecyl)phthalate, (n-propyl)(isoundecyl) phthalate, (n-propyl)(n-dodecyl)phthalate, (n-propyl) (isododecyl) phthalate, (n-propyl)(n-tridecyl)phthalate, (n-propyl)(isotridecyl) phthalate, (n-propyl)(n-tetradecyl)phthalate, (n-propyl)(isotetradecyl) phthalate, (n-propyl)(n-pentadecyl) phthalate, (n-propyl)(isopentadecyl) phthalate,(n-propyl)(n-hexadecyl) phthalate, (n-propyl) (isohexadecyl) phthalate,(n-propyl)(n-heptadecyl) phthalate, (n-propyl)(isoheptadecyl) phthalate,(n-propyl) (n-octadecyl) phthalate, (n-propyl)(isooctadecyl) phthalate,(isopropyl)(cyclohexyl) phthalate, (isopropyl)(n-heptyl) phthalate,(isopropyl)(isoheptyl) phthalate, (isopropyl) (n-octyl) phthalate,(isopropyl)(2-ethylhexyl) phthalate, (isopropyl)(isooctyl) phthalate,(isopropyl)(2-octyl) phthalate, (isopropyl)(n-nonyl) phthalate,(isopropyl) (isononyl) phthalate, (isopropyl)(3,5,5-trimethylhexyl)phthalate, (isopropyl)(n-decyl) phthalate, (isopropyl) (isodecyl)phthalate, (isopropyl)(n-undecyl) phthalate, (isopropyl)(isoundecyl)phthalate, (isopropyl)(n-dodecyl) phthalate, (isopropyl)(isododecyl)phthalate, (isopropyl) (n-tridecyl) phthalate, (isopropyl)(isotridecyl)phthalate, (isopropyl)(n-tetradecyl) phthalate, (isopropyl)(isotetradecyl) phthalate, (isopropyl)(n-pentadecyl) phthalate,(isopropyl)(isopentadecyl) phthalate, (isopropyl)(n-hexadecyl)phthalate, (isopropyl) (isohexadecyl) phthalate,(isopropyl)(n-heptadecyl) phthalate, (isopropyl)(isoheptadecyl)phthalate, (isopropyl)(n-octadecyl) phthalate, (isopropyl)(isooctadecyl) phthalate, (n-butyl)(cyclohexyl) phthalate,(n-butyl)(n-heptyl) phthalate, (n-butyl)(isoheptyl) phthalate,(n-butyl)(n-octyl) phthalate, (n-butyl)(2-ethylhexyl) phthalate,(n-butyl)(isooctyl) phthalate, (n-butyl)(2-octyl) phthalate,(n-butyl)(n-nonyl) phthalate, (n-butyl)(isononyl) phthalate,(n-butyl)(3,5,5-trimethylhexyl) phthalate, (n-butyl)(n-decyl) phthalate,(n-butyl)(isodecyl) phthalate, (n-butyl)(n-undecyl) phthalate,(n-butyl)(isoundecyl) phthalate, (n-butyl)(n-dodecyl) phthalate,(n-butyl)(isododecyl) phthalate, (n-butyl)(n-tridecyl) phthalate,(n-butyl)(isotridecyl) phthalate, (n-butyl)(n-tetradecyl) phthalate,(n-butyl)(isotetradecyl) phthalate, (n-butyl)(n-pentadecyl) phthalate,(n-butyl)(isopentadecyl) phthalate, (n-butyl)(n-hexadecyl) phthalate,(n-butyl)(isohexadecyl) phthalate, (n-butyl)(n-heptadecyl) phthalate,(n-butyl)(isoheptadecyl) phthalate, (n-butyl)(n-octadecyl) phthalate,(n-butyl)(isooctadecyl) phthalate, (isobutyl)(cyclohexyl) phthalate,(isobutyl)(n-heptyl) phthalate, (isobutyl)(isoheptyl) phthalate,(isobutyl)(n-octyl) phthalate, (isobutyl)(2-ethylhexyl) phthalate,(isobutyl)(isooctyl) phthalate, (isobutyl)(2-octyl) phthalate,(isobutyl)(n-nonyl) phthalate, (isobutyl)(isononyl) phthalate,(isobutyl)(3,5,5-trimethylhexyl) phthalate, (isobutyl)(n-decyl)phthalate, (isobutyl)(isodecyl) phthalate, (isobutyl)(n-undecyl)phthalate, (isobutyl)(isoundecyl) phthalate, (isobutyl)(n-dodecyl)phthalate, (isobutyl)(isododecyl) phthalate, (isobutyl)(n-tridecyl)phthalate, (isobutyl)(isotridecyl) phthalate, (isobutyl)(n-tetradecyl)phthalate, (isobutyl) (isotetradecyl) phthalate,(isobutyl)(n-pentadecyl) phthalate, (isobutyl)(isopentadecyl) phthalate,(isobutyl)(n-hexadecyl) phthalate, (isobutyl)(isohexadecyl) phthalate,(isobutyl)(n-heptadecyl) phthalate, (isobutyl)(isoheptadecyl) phthalate,(isobutyl)(n-octadecyl) phthalate, (isobutyl)(isooctadecyl) phthalate,(sec-butyl)(cyclohexyl) phthalate, (sec-butyl)(n-heptyl) phthalate,(sec-butyl)(isoheptyl) phthalate, (sec-butyl)(n-octyl) phthalate,(sec-butyl)(2-ethylhexyl) phthalate, (sec-butyl)(isoctyl) phthalate,(sec-butyl)(2-octyl) phthalate, (sec-butyl)(n-nonyl) phthalate,(sec-butyl)(isononyl) phthalate, (sec-butyl)(3,5,5-trimethylhexyl)phthalate, (sec-butyl)(n-decyl) phthalate, (sec-butyl)(isodecyl)phthalate, (sec-butyl)(n-undecyl) phthalate, (sec-butyl)(isoundecyl)phthalate, (sec-butyl)(n-dodecyl) phthalate, (sec-butyl)(isododecyl)phthalate, (sec-butyl)(n-tridecyl) phthalate, (sec-butyl)(isotridecyl)phthalate, (sec-butyl)(n-tetradecyl) phthalate,(sec-butyl)(isotetradecyl) phthalate, (sec-butyl)(n-pentadecyl)phthalate, (sec-butyl)(isopentadecyl) phthalate,(sec-butyl)(n-hexadecyl) phthalate, (sec-butyl)(isohexadecyl) phthalate,(sec-butyl)(n-heptadecyl) phthalate, (sec-butyl)(isoheptadecyl)phthalate, (sec-butyl)(n-octadecyl) phthalate, (sec-butyl)(isooctadecyl)phthalate, and recommended are preferably (n-propyl)(cyclohexyl)phthalate, (n-propyl)(isoheptyl) phthalate, (n-propyl)(2-ethylhexyl)phthalate, (n-propyl)(isooctyl) phthalate, (n-propyl)(2-octyl)phthalate, (n-propyl)(isononyl) phthalate,(n-propyl)(3,5,5-trimethylhexyl) phthalate, (n-propyl)(isodecyl)phthalate, (n-propyl)(isoundecyl) phthalate, (n-propyl)(isododecyl)phthalate, (n-propyl)(isotridecyl) phthalate, (n-propyl)(isotetradecyl)phthalate, (n-propyl)(isopentadecyl) phthalate, (n-propyl)(isohexadecyl)phthalate, (n-propyl)(isoheptadecyl) phthalate, (n-propyl)(isooctadecyl)phthalate, (isopropyl)(cyclohexyl) phthalate, (isopropyl)(isoheptyl)phthalate, (isopropyl)(2-ethylhexyl) phthalate, (isopropyl)(isooctyl)phthalate, (isopropyl)(2-octyl) phthalate, (isopropyl)(isononyl)phthalate, (isopropyl)(3,5,5-trimethylhexyl) phthalate,(isopropyl)(isodecyl) phthalate, (isopropyl)(isoundecyl) phthalate,(isopropyl)(isododecyl) phthalate, (isopropyl)(isotridecyl) phthalate,(isopropyl)(isotetradecyl) phthalate, (isopropyl)(isopentadecyl)phthalate, (isopropyl)(isohexadecyl) phthalate,(isopropyl)(isoheptadecyl) phthalate, (isopropyl)(isooctadecyl)phthalate, (n-butyl)(cyclohexyl) phthalate, (n-butyl)(isoheptyl)phthalate, (n-butyl)(2-ethylhexyl) phthalate, (n-butyl)(isooctyl)phthalate, (n-butyl)(2-octyl) phthalate, (n-butyl)(isononyl) phthalate,(n-butyl)(3,5,5-trimethylhexyl) phthalate, (n-butyl)(isodecyl)phthalate, (n-butyl)(isoundecyl) phthalate, (n-butyl)(isododecyl)phthalate, (n-butyl)(isotridecyl) phthalate, (n-butyl)(isotetradecyl)phthalate, (n-butyl) (isopentadecyl) phthalate, (n-butyl) (isohexadecyl)phthalate, (n-butyl)(isoheptadecyl) phthalate, (n-butyl)(isooctadecyl)phthalate, (isobutyl)(cyclohexyl) phthalate, (isobutyl)(isoheptyl)phthalate, (isobutyl)(2-ethylhexyl) phthalate, (isobutyl)(isooctyl)phthalate, (isobutyl)(2-octyl) phthalate, (isobutyl)(isononyl)phthalate, (isobutyl)(3,5,5-trimethylhexyl) phthalate,(isobutyl)(isodecyl) phthalate, (isobutyl)(isoundecyl) phthalate,(isobutyl)(isododecyl) phthalate, (isobutyl)(isotridecyl) phthalate,(isobutyl)(isotetradecyl) phthalate, (isobutyl)(isopentadecyl)phthalate, (isobutyl)(isohexadecyl) phthalate, (isobutyl)(isoheptadecyl)phthalate, (isobutyl)(isooctadecyl) phthalate, (sec-butyl)(cyclohexyl)phthalate, (sec-butyl)(isoheptyl) phthalate, (sec-butyl)(2-ethylhexyl)phthalate, (sec-butyl)(isooctyl)phthalate, (sec-butyl)(2-octyl)phthalate, (sec-butyl)(isononyl) phthalate,(sec-butyl)(3,5,5-trimethylhexyl) phthalate, (sec-butyl)(isodecyl)phthalate, (sec-butyl)(isoundecyl) phthalate, (sec-butyl)(isododecyl)phthalate, (sec-butyl)(isotridecyl) phthalate,(sec-butyl)(isotetradecyl) phthalate, (sec-butyl) (isopentadecyl)phthalate, (sec-butyl)(isohexadecyl) phthalate,(sec-butyl)(isoheptadecyl) phthalate, (sec-butyl)(isooctadecyl)phthalate.

Among the foregoing alicyclic or aromatic adjacent dicarboxylic acidmixed diesters, the alicyclic adjacent dicarboxylic mixed diestersrepresented by the formula (4) wherein A is a cyclohexane ring or acyclohexene ring has a high hydrolysis stability and is preferred. Amongsuch alicyclic adjacent dicarboxylic acid mixed diesters represented bythe formula (4), preferable are those wherein R⁵ is a straight-chainalkyl group having 1 to 5 carbon atoms or a branched-chain alkyl grouphaving 3 to 5 carbon atoms, and R⁶ is a straight-chain or branched chainalkyl group having 6 to 11 carbon atoms. Particularly preferable arealicyclic adjacent dicarboxylic acid mixed diesters represented by theformula (4) wherein A is a cyclohexane ring or cyclohexene ring, X is ahydrogen atom, R⁵ is a straight-chain alkyl group having 1 to 5 carbonatoms or a branched-chain alkyl group having 3 to 5 carbon atoms, and R⁶is a straight-chain or branched chain alkyl group having 6 to 11 carbonatoms.

When A is a cyclohexene ring, the group —COOR⁵ and the group —COOR⁶ arepreferably present at the 1- and 2-positions and the double bond ispresent between the 4- and 5-positions.

Among them, more preferred in view of hydrolysis stability, heatstability, miscibility with a refrigerant, electrical insulatingproperty and lubricity are (isopropyl) (2-ethylhexyl)1,2-cyclohexanedicarboxylate, (isopropyl) (isononyl)1,2-cyclohexanedicarboxylate, (isopropyl) (3,5,5-trimethylhexyl)1,2-cyclohexanedicarboxylate, (isobutyl) (2-ethylhexyl)1,2-cyclohexanedicarboxylate, (isobutyl) (isononyl)1,2-cyclohexanedicarboxylate, (isobutyl) (3,5,5-trimethylhexyl)1,2-cyclohexanedicarboxylate, (isopropyl) (2-ethylhexyl)4-cylochexene-1,2-dicarboxylate, (isopropyl) (isononyl)4-cyclohexene-1,2-dicarboxylate, (isopropyl) (3,5,5-trimethylhexyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl) (2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate, (isobutyl) (isononyl)4-cyclohexene-1,2-dicarboxylate, and (isobutyl) (3,5,5-trimethylhexyl)4-cyclohexene-1,2-dicarboxylate.

The cyclohexane adjacent dicarboxylic acid mixed diester can also beprepared by completely hydrogenating the aromatic ring of the aromaticadjacent dicarboxylic acid mixed diester of the invention (hydrogenationof nucleus). The cyclohexene adjacent dicarboxylic acid mixed diestercan be prepared by partly hydrogenating the aromatic ring of thearomatic adjacent dicarboxylic acid mixed diester.

The alicyclic adjacent dicarboxylic acid mixed diesters of the inventioninclude position isomers ascribed to ester groups. For example,4-cyclohexene-1,2-dicarboxylic acid diester may be an isomer dependingon whether two ester groups are present in equatorial or axialpositions. Specifically, the diester is a cis isomer when one of its twoester groups is in the equatorial position and the other is present inthe axial position. The diester is a trans isomer when both of its twoester groups are present in the equatorial position or in the axialposition. All of these isomers can be used for use in a refrigeratoroil.

When esterification temperature is set to higher than 210° C. and up toabout 230° C. in the second stage esterification for the preparation ofthe alicyclic adjacent dicarboxylic acid mixed diester, theesterification tends to predominantly give a trans isomer, whereas whenesterification temperature is set at about 160 to about 210° C., theesterification tends to predominantly give a cis isomer.

A cis-form ester can be isomerized to a trans-form ester. Isomerizationcan be performed according to the method disclosed, for example, in U.S.Pat. No. 5,231,218.

As to the ratio of the isomers, it is desirable that trans isomer/cisisomer ratio is 0/100 to 80/20 (by area % as determined by gaschromatography). More preferably, the trans isomer/cis isomer ratio is20/80 to 80/20 (by area % as determined by gas chromatography) in viewof hydrolysis stability, electrical insulating property and miscibilitywith a refrigerant. The conditions under which gas chromatography isconducted will be described in Examples.

Process for Preparing an Ester of Embodiment II

Step (a): First-Stage Esterification Reaction

The alicyclic or aromatic adjacent dicarboxylic anhydride to be used asthe raw material (hereinafter referred to as “acid component 1”) isrepresented by the formula (5s)

wherein A and X are as defined above, and examples thereof are1,2-cyclohexanedicarboxylic anhydride, cyclohexene-1,2-dicarboxylicanhydride, methyl-substituted 1,2-cyclohexanedicarboxylic anhydride,methyl-substituted cyclohexene-1,2-dicarboxylic anhydride and phthalicanhydride.

While the position of double bond in cyclohexenedicarboxylic acid may beany position relative to its acid anhydride group (—CO—O—CO—) withoutspecific limitation, from the standpoint of hydrolysis stability, onewherein the acid anhydride group (—CO—O—CO—) is attached to the1,2-positions and the double bond is present between 4- and 5-positionsis preferable.

Specific examples of the alicyclic or aromatic adjacent dicarboxylicanhydride to be used herein are 1,2-cyclohexanedicarboxylic anhydride,4-cyclohexene-1,2-dicarboxylic anhydride, 1-cyclohexene-1,2-dicarboxylicanhydride, 3-methyl-1,2-cyclohexanedicarboxylic anhydride,4-methyl-1,2-cyclohexanedicarboxylic anhydride,3-methyl-4-cyclohexene-1,2-dicarboxylic anhydride,4-methyl-4-cyclohexene-1,2-dicarboxylic anhydride and phthalic anhyride.

In esterification, the above alicyclic or aromatic adjacent dicarboxylicanhydrides can be used either alone or in combination.

In carrying out the first-stage esterification reaction, “alcoholcomponent 1” is used in an amount of 0.5 to 1.5 moles, preferably 0.8 to1.2 moles, per mole of acid component 1. “Alcohol component 1” may be asingle alcohol or an alcohol mixture. “Alcohol component 1” comprises amonohydric alcohol of 1 to 5 carbon atoms (P) and optionally amonohydric alcohol of 6 to 18 carbon atoms (Q) wherein (P):(Q) moleratio is 0.1:99.9 to 100:0 (mole ratio). It is recommended that the moleratio of the monohydric alcohol of 1 to 5 carbon atoms (P):themonohydric alcohol of 6 to 18 carbon atoms (Q) is preferably(P):(Q)=5:95 to 100:0 (mole ratio), in particular (P):(Q)=40:60 to100:0.

The first-stage esterification reaction can be effected in the absenceof a catalyst or in the presence of a sulfur-free and phosphorus-freecatalyst, preferably in the absence of a catalyst.

The sulfur-free and phosphorus-free catalyst for use is a catalyst whichdo not contain a sulfur element and a phosphorus element in the elementsconstituting the catalyst. Specifically, examples of the catalyst areLewis acids and alkali metals, etc. which do not contain a sulfurelement or a phosphorus element. More specifically, examples of Lewisacids are aluminum derivatives, tin derivatives, titanium derivatives,lead derivatives and zinc derivatives. Examples of alkali metals aresodium alkoxide, potassium alkoxide, sodium hydroxide, potassiumhydroxide, etc. These catalysts can be used either alone or incombination. Preferred catalysts are those which also do not contain asulfur element and phosphorus element as impurities.

Among such catalysts, it is particularly preferable to use tetra(C₃-C₈alkyl) titanate, titanium oxide, titanium hydroxide, sodium alkoxide of1 to 4 carbon atoms, sodium hydroxide, C₃-C₁₂ fatty acid tin salt, tinoxide, tin hydroxide, zinc oxide, zinc hydroxide, lead oxide, leadhydroxide, aluminum oxide and aluminum hydroxide. The amount of thecatalyst to be used is, for example, about 0.05 to about 1 wt. % basedon the total amount of acid component 1 and alcohol component 1 used asthe raw materials for synthesis of the ester.

The reaction temperature for the first-stage esterification is, forexample, 110 to 150° C. and the reaction is usually carried out for 0.5to 3 hours.

In the first-stage esterification reaction, theoretically 1 mole of theacid anhydride can react with 1 mole of “alcohol component 1” to givethe alicyclic or aromatic adjacent dicarboxylic acid monoester of theformula (5). In the course of the reaction, there is produced a smallamount of a diester such as alicyclic or aromatic adjacent dicarboxylicacid mixed diester. In other words, actually the reaction product offirst-stage esterification reaction may contain a diester in addition tothe monoester of the formula (5). Possibly the reaction product furthercontains the acid anhydride, dicarboxylic acid, and alcohol used as theraw materials. In the specification, the term “a first reaction mixture”is used to include the above reaction product possibly containing thesesubstances. The composition thereof can be analyzed by gaschromatography.

The reaction pressure in the esterification reaction is not particularlylimited, and may be atmospheric pressure or reduced pressure (e.g., 133to 66500 Pa). However, it is recommended to carry out the esterificationreaction under atmospheric pressure from the standpoint of giving thealicyclic or aromatic adjacent dicarboxylic acid monoester representedby the formula (5) with high selectivity.

When an oxide, peroxide, carbonyl compound and like oxygen-containingorganic compounds are produced in the exterification reaction due tooxidative deterioration of the raw materials, the obtained ester and theorganic solvent (water-entraining agent), the hygroscopicity, hydrolysisstability and electrical insulating property would be adverselyaffected. Consequently, the reaction is preferably carried out in anatmosphere or stream of inert gas such as nitrogen gas.

Step (b): Second-Stage Esterification Reaction

The first reaction mixture containing the alicyclic or aromatic adjacentdicarboxylic acid monoester of the formula (5) prepared in thefirst-stage is esterified with “alcohol component 2” to produce areaction mixture (hereinafter referred to as “a second reactionmixture”) containing an alicyclic or aromatic adjacent dicarboxylic acidmixed diester of the formula (4).

The second-stage esterification reaction can be conducted after thealicyclic or aromatic adjacent dicarboxylic acid monoester of theformula (5) is isolated from the reaction product. The isolation can beperformed by conventional methods such as distillation, liquid-liquidextraction, column chromatography or the like. However, in view ofeconomy, it is desirable to continuously conduct the first-stage andsecond-stage esterification reactions without isolation of the alicyclicor aromatic adjacent dicarboxylic acid monoester of the formula (5).

Specific examples of the alicyclic or aromatic adjacent dicarboxylicacid monoester of the formula (5) are monomethyl1,2-cyclohexanedicarboxylate, monoethyl 1,2-cyclohexanedicarboxylate,mono(n-propyl) 1,2-cyclohexanedicarboxylate, monoisopropyl1,2-cyclohexanedicarboxylate, mono(n-butyl)1,2-cyclohexanedicarboxylate, monoisobutyl 1,2-cyclohexanedicarboxylate,mono(sec-butyl) 1,2-cyclohexanedicarboxylate, mono(n-heptyl)1,2-cyclohexanedicarboxylate, monoisoheptyl1,2-cyclohexanedicarboxylate, mono(n-octyl)1,2-cyclohexanedicarboxylate, mono(2-ethylhexyl)1,2-cyclohexanedicarboxylate, mono(2-octyl)1,2-cyclohexanedicarboxylate, monoisooctyl 1,2-cyclohexanedicarboxylate,mono(n-nonyl) 1,2-cyclohexanedicarboxylate, monoisononyl1,2-cyclohexanedicarboxylate, mono(3,5,5-trimethylhexyl)1,2-cyclohexanedicarboxylate, mono(n-decyl)1,2-cyclohexanedicarboxylate, monoisodecyl 1,2-cyclohexanedicarboxylate,mono(n-undecyl) 1,2-cyclohexanedicarboxylate, monoisoundecyl1,2-cyclohexanedicarboxylate, mono(n-dodecyl)1,2-cyclohexanedicarboxylate, monoisododecyl1,2-cyclohexanedicarboxylate, mono(n-tridecyl)1,2-cyclohexanedicarboxylate, monoisotridecyl1,2-cyclohexanedicarboxylate, mono(n-tetradecyl)1,2-cyclohexanedicarboxylate, monoisotetradecyl1,2-cyclohexanedicarboxylate, mono(n-pentadecyl)1,2-cyclohexanedicarboxylate, monoisopentadecyl1,2-cyclohexanedicarboxylate, mono(n-hexadecyl)1,2-cyclohexanedicarboxylate, monoisohexadecyl1,2-cyclohexanedicarboxylate, mono(n-heptadecyl)1,2-cyclohexanedicarboxylate, monoisoheptadecyl1,2-cyclohexanedicarboxylate, mono(n-octadecyl)1,2-cyclohexanedicarboxylate, monoisooctadecyl1,2-cyclohexanedicarboxylate, monocyclohexyl1,2-cyclohexanedicarboxylate, monomethyl4-cyclohexene-1,2-dicarboxylate, monoethyl4-cyclohexene-1,2-dicarboxylate, mono(n-propyl)4-cyclohexene-1,2-dicarboxylate, monoisopropyl4-cyclohexene-1,2-dicarboxylate, mono(n-butyl)4-cyclohexene-1,2-dicarboxylate, monoisobutyl4-cyclohexene-1,2-dicarboxylate, mono(sec-butyl)4-cyclohexene-1,2-dicarbosylate, mono(n-heptyl)4-cyclohexene-1,2-dicarboxylate, monoisoheptyl4-cyclohexene-1,2-dicarboxylate, mono(n-octyl)4-cyclohexene-1,2-dicarboxylate, mono(2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate, mono(2-octyl)4-cyclohexene-1,2-dicarboxylate, monoisooctyl4-cyclohexene-1,2-dicarboxylate, mono(n-nonyl)4-cyclohexene-1,2-dicarboxylate, monoisononyl4-cyclohexene-1,2-dicarboxylate, mono(3,5,5-trimethylhexyl)4-cyclohexene-1,2-dicarboxylate, mono(n-decyl)4-cyclohexene-1,2-dicarboxylate, monoisodecyl4-cyclohexene-1,2-dicarboxylate, mono(n-undecyl)4-cyclohexene-1,2-dicarboxylate, monoisoundecyl4-cyclohexene-1,2-dicarboxylate, mono(n-dodecyl)4-cyclohexene-1,2-dicarboxylate, monoisododecyl4-cyclohexene-1,2-dicarboxylate, mono(n-tridecyl)4-cyclohexene-1,2-dicarboxylate, monoisotridecyl4-cyclohexene-1,2-dicarboxylate, mono(n-tetradecyl)4-cyclohexene-1,2-dicarboxylate, monoisotetradecyl4-cyclohexene-1,2-dicarboxylate, mono(n-pentadecyl)4-cyclohexene-1,2-dicarboxylate, monoisopentadecyl4-cyclohexene-1,2-dicarboxylate, mono(n-hexadecyl)4-cyclohexene-1,2-dicarboxylate, monoisohexadecyl4-cyclohexene-1,2-dicarboxylate, mono(n-heptadecyl)4-cyclohexene-1,2-dicarboxylate, monoisoheptadecyl4-cyclohexene-1,2-dicarboxylate, mono(n-octadecyl)4-cyclohexene-1,2-dicarboxylate, monoisooctadecyl4-cyclohexene-1,2-dicarboxylate,monocyclohexyl-4-cyclohexene-1,2-dicarboxylate, monomethyl phthalate,monoethyl phthalate, mono(n-propyl) phthale, monoisopropyl phthalate,mono(n-butyl) phthalate, monoisobutyl phthalate, mono(sec-butyl)phthalate, mono(n-heptyl) phthalate, monoisoheptyl phthalate,mono(n-octyl) phthalate, mono(2-ethylhexyl) phthalate, mono(2-octyl)phthalate, monoisooctyl phthalate, mono(n-nonyl) phthalate, monoisononylphthalate, mono(3,5,5-trimethylhexyl) phthalate, mono(n-decyl)phthalate, monoisodecyl phthalate, mono(n-undecyl) phthalate,monoisoundecyl phthalate, mono(n-dodecyl) phthalate, monoisododecylphthalate, mono(n-tridecyl) phthalate, monoisotridecyl phthalate,mono(n-tetradecyl) phthalate, monoisotetradecyl phthalate,mono(n-pentadecyl) phthalate, monoisopentadecyl phthalate,mono(n-hexadecyl) phthalate, monoisohexadecyl phthalate,mono(n-heptadecyl) phthalate, monoisoheptadecyl phthalate,mono(n-octadecyl) phthalate, monoisooctadecyl phthalate, monocyclohexylphthalate, etc.

In the alicyclic or aromatic adjacent dicarboxylic acid monoester of theformula (5), the positions of the ester group and free carboxylic acidgroup are not limited. Thus, for example, when the ester group ispresent at the 1-position, the free carboxylic acid group is present inthe 2-position, and when the ester group is present at the 2-position,the free carboxylic acid group is present in the 1-position.

The first reaction mixture containing the alicyclic or aromatic adjacentdicarboxylic acid monoester of the formula (5) further contains, forexample in the case of isobutyl ester, monoisobutyl1,2-cyclohexanedicarboxylate, diisobutyl 1,2-cyclohexanedicarboxylate,isobutanol, 1,2-cyclohexanedicarboxlic anhydride,1,2-cyclohexanedicarboxylic acid, etc.

In the second stage esterification reaction, “alcohol component 2” isused. “Alcohol component 2” may be a single alcohol or a mixture ofalcohols, and comprises a monohydric alcohol of 6 to 18 carbon atoms (T)and optionally a monohydric alcohol of 1 to 5 carbon atoms (S) wherein(S):(T) mole ratio is 0:100 to 99.9:0.1 (mole ratio). It is recommendedthat the mole ratio of the monohydric alcohol of 1 to 5 carbon atoms(S):the monohydric alcohol of 6 to 18 carbon atoms (T) is (S):(T)=0:100to 95:5 (mole ratio), especially (S):(T)=0:100 to 40:60 (mole ratio).

Examples of the monohydric alcohol of 1 to 5 carbon atoms (S) aremethanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol,sec-butanol, n-pentanol, isopentanol and like aliphatic monohydricalcohols of 1 to 5 carbon atoms, cyclopropanol, cyclobutanol,cyclopentanol and like alicyclic monohydric alcohols of 3 to 5 carbonatoms and the like. These alcohols can be used either alone or incombination. Among them, monohydric alcohols of 3 to 5 carbon atoms arepreferable to improve the lubricity.

Examples of the monohydric alcohol of 6 to 18 carbon atoms (T) to beused herein are n-hexanol, isohexanol, n-heptanol, 2-methylhexanol,isoheptanol, n-octanol, 2-ethylhexanol, 2-octanol, isooctanol,2-methylheptanol, n-nonanol, isononanol, 3,5,5-trimethylhexanol,2,6-dimethyl-4-heptanol, n-decanol, isodecanol, n-undecanol,isoundecanol, n-dodecanol, isododecanol, n-tridecanol, isotridecanol,n-tetradecanol, isotetradecanol, n-pentadecanol, isopentadecanol,n-hexadecanol, isohexadecanol, n-heptadecanol, isoheptadecanol,n-octadecanol, isooctadecanol, hexenol, 5-hexenol, 2-heptenol,6-heptenol, 2-octenol, 8-nonenol, 2-decenol, 2-undecenol, 10-undecenol,11-dodecenol, 12-tridecenol, 2-tetradecenol, 2-pentadecenol,2-hexadecenol, 15-hexadecenol, 2-heptadecenol, 2-octadecenol,9-octadecenol and like aliphatic monohydric alcohols of 6 to 18 carbonatoms, cyclohexanol, methylcyclohexanol, dimethyl-cyclohexanol and likealicyclic monohydric alcohols of 6 to 10 carbon atoms. These alcoholscan be used either alone or in combination. Among them, to improvemiscibility with a refrigerant, saturated aliphatic monohydric alcoholsof 6 to 11 carbon atoms are preferably used and branched-chain saturatedaliphatic monohydric alcohols of 6 to 11 carbon atoms are morepreferably used.

The amount of “alcohol component 2” to be used in the second-stageesterification reaction can not be particularly limited because it isvariable depending on the amount of free carboxylic acid group in thefirst reaction mixture containing alicyclic or aromatic adjacentdicarboxylic acid monoester of the formula (5). The amount thereof isproper if it is sufficient to quantitatively give the contemplated mixeddiester. For example, “alcohol component 2” may be used in an amount of1 to 1.5 moles per mole of the monoester of the formula (5) in the firstreaction mixture. The amount of the monoester in the first reactionmixture can be calculated by measuring the total acid number of thefirst reaction mixture.

Alternatively, when the first-stage reaction and the second-stagereaction are consecutively carried out without isolating the monoesterof the formula (5) obtained in the first-stage, “alcohol component 2”may be used in an amount such that the total amount of “alcoholcomponent 1” and “alcohol component 2” is 2.0 to 2.5 moles, preferably2.0 to 2.1 moles, per mole of “acid component 1”. For example, when theamount of “alcohol component 1” to be used is 0.5 to 1.5 moles, theamount of “alcohol component 2” is 0.5 to 1.0 mole.

In order to avoid decrease in the reaction velocity due to a suddendecrease in the reaction temperature, it is preferable to gradually addalcohol component 2.

The reaction temperature for the second-stage esterification reactionis, e.g., 160 to 230° C. Usually the reaction is completed in 2 to 20hours.

It is recommended that alcohol component 1 and alcohol component 2 to beused in esterification preferably have a peroxide value of preferably1.0 meq/kg or less, more preferably 0.5 meg/kg or less. Furthermore, itis recommended that these alcohol components have a carbonyl value ofpreferably 15 or less, more preferably 5 or less, most preferably 1 orless.

When the ester is prepared using an alcohol having a peroxide value of1.0 meq/kg or less and a carbonyl value of 5 or less, the obtained estershows excellent properties as a refrigerator oil. When the ester isprepared using alcohols having a peroxide value of 1.0 meq/kg or lessand a carbonyl value of 1 or less, the obtained ester shows markedlysuperior properties as a refrigerator oil.

The term “peroxide value” used herein is described in 2.5.2-1996 ofStandard Methods for the Analysis of Fats, Oil and Related Materials(Japan Oil Chemists' Society), and refers to an amount of iodinereleased by addition of potassium iodide to a sample and expressed inmilliequivalent per kilogram of the sample, according to the methoddescribed therein.

The term “carbonyl value” used herein is described in 2.5.4-1996 ofStandard Methods for the Analysis of Fats, Oil and Related Materials(Japan Oil Chemists' Society), and refers to a value obtained by causing2,4-dinitrophenylhydrazine to act on a sample and converting the valueof its absorbance at 440 nm to a value per gram of the sample, accordingto the method described therein.

When an alcohol having a peroxide value of 1.0 meq/kg or less is used,the obtained alicyclic or aromatic dicarboxylic acid mixed diester isless adversely affected in properties such as hue, total acid number andperoxide value and is excellent in the properties such as electricalinsulating property, heat stability and hydrolysis stability.

An alcohol having a peroxide value of 1.0 meq/kg or less can be preparedby purifying an alcohol having a peroxide value of more than 1.0 meq/kgthrough distillation or through a treatment with a reducing agent tothereby decrease the peroxide value.

Generally an alcohol immediately after distillation has a peroxide valueof 1.0 meq/kg or less. However, such alcohol may show a peroxide valueof more than 1.0 meq/kg due to oxidation during a long-term storage(e.g. storage for 6 months or longer) depending on the storageconditions. Therefore, it is necessary to confirm a peroxide value ofthe alcohol before esterification.

The purification by distillation can be performed, e.g. by distilling analcohol having a peroxide value exceeding 1.0 meq/kg at 50-300° C. inthe presence of an alkali compound under reduced pressure. Useful alkalicompounds include, for example, NaOH, KOH, LiOH, etc. It isrecommendable to use the alkali compound in an amount of 0.001 to 0.5wt. % based on the alcohol.

The purification by reduction can be conducted, e.g. by stirring analcohol having a peroxide value exceeding 1.0 meq/kg at 30-150° C. inthe presence of a reducing agent for 30 minutes to 5 hours, preferably 1to 2 hours. Useful reducing agents include, for example, sodiumborohydride, potassium borohydride, lithium borohydride, lithiumaluminum hydride, etc. It is recommendable to use the reducing agent inan amount of 30 to 10,000 ppm based on the alcohol.

When an alicyclic dicarboxylic acid diester is prepared using an alcoholhaving a carbonyl value of 15 or less, preferably 5 or less, morepreferably 1 or less, the obtained ester has excellent hue and reducedperoxide value.

In the case of an alcohol having a carbonyl value of more than 15 aswell, its carbonyl value can be decreased to 15 or less by purificationthrough distillation or by purification through reduction, which may becarried out following the procedure of the foregoing method for loweringthe peroxide value.

The second-stage esterification reaction may be carried out in theabsence of a catalyst or in the presence of a sulfur-free andphosphorus-free catalyst. However, it is recommended to carry out theesterification reaction in the presence of a sulfur-free andphosphorus-free catalyst.

The sulfur-free and phosphorus-free catalyst is a catalyst which doesnot contain a sulfur element or a phosphorus element in the elementsconstituting the catalyst. Specifically, examples of the catalyst areLewis acids and alkali metals, etc. which contain neither a sulfurelement nor a phosphorus element. More specifically, examples of Lewisacids are aluminum derivatives, tin derivatives, titanium derivatives,lead derivatives and zinc derivatives. Examples of alkali metals aresodium alkoxide, potassium alkoxide, sodium hydroxide, potassiumhydroxide, etc. These catalysts can be used either alone or incombination. Preferred catalysts are those which do not contain a sulfurelement and a phosphorus element as the impurities.

Among such catalysts, it is particularly preferable to use tetra(C₃-C₈alkyl) titanate, titanium oxide, titanium hydroxide, sodium alkoxide of1 to 4 carbon atoms, sodium hydroxide, C₃-C₁₂ fatty acid tin salt, tinoxide, tin hydroxide, zinc oxide, zinc hydroxide, lead oxide, leadhydroxide, aluminum oxide and aluminum hydroxide. The amount of thecatalyst to be used is, for example, about 0.05 to about 1 wt. % basedon the total amount of the first reaction mixture and alcohol component2.

To accelerate the distillation of water generated by the reaction inesterification, a water-entraining agent such as benzene, toluene,xylene, cyclohexane or the like may be used in esterification.

The esterification reaction may be carried out under atmosphericpressure or under reduced pressure (e.g., 133 to 66500 Pa). However,from a viewpoint of accelerating the esterification reaction, it ispreferable to combine esterification reaction under atmospheric pressureand esterification reaction under reduced pressure. Particularly, it isrecommended to carry out the esterification reaction under reducedpressure in a later stage of the reaction (such as the stage in whichthe total acid number of the reaction mixture becomes about 10 mgKOH/gor less) when the esterification reaction velocity becomes low.

When an oxide, peroxide, carbonyl compound and like oxygen-containingorganic compounds are produced due to oxidative deterioration of the rawmaterials, the obtained ester and the organic solvent (water-entrainingagent) in the esterification reaction, the hygroscopicity, hydrolysisstability and electrical insulating property would be adverselyaffected. Consequently, the esterification reaction is preferablycarried out in an atmosphere or stream of inert gas such as nitrogengas.

In the preparation of the alicyclic or aromatic dicarboxylic acid mixeddiester represented by the formula (4) of the present invention, whenthe proportion of an monohydric alcohol of 1 to 5 carbon atoms [(P)+(S)]is 10 to 90 mole %, relative to the total amount [(P)+(Q)+(S)+(T)] ofalcohol component 1 [(P)+(Q)] used in the first-stage esterificationreaction and alcohol component 2 [(S)+(T)] used in the second-stageesterification reaction, it is recommended, from the standpoint ofreducing the reaction time,

-   -   1) to use the whole amount of the monohydric alcohol of 1 to 5        carbon atoms as (P) in the first-stage esterification reaction        and to use 0 mole % of said alcohol in the second-stage        esterification reaction, when said proportion of the monohydric        alcohol of 1 to 5 carbon atoms [(P)+(S)] is not less than 10        mole % and not greater than 50 mole %, and    -   2) to use the monohydric alcohol of 1 to 5 carbon atoms as (P)        in an amount of 50 mole % relative to the total alcohol amount        [(P)+(Q)+(S)+(T)] in the first-stage esterification reaction and        to use the rest of said monohydric alcohol of 1 to 5 carbon        atoms as (S) in the second-stage esterification reaction, when        said proportion of the monohydric alcohol of 1 to 5 carbon atoms        [(P)+(S)] is more than 50 mole % and not more than 90 mole %.

When the alicyclic or aromatic adjacent dicarboxylic acid mixed diesterrepresented by the formula (4) is prepared by the process of the presentinvention, two species of esters represented by the formula (6) areconcurrently produced as by-products, but no problem arises even if thereaction product contains such ester compounds.

wherein X, A and R⁵ are as defined above, two R⁵ are the same, and thetwo —COOR⁵ groups are attached to two adjacent carbon atoms of acyclohexane ring, a cyclohexene ring or a benzene ring;

When using, e.g. a monohydric alcohol of 1 to 5 carbon atoms (R^(5a)OH)as alcohol component 1 and a monohydric alcohol of 6 to 18 carbon atoms(R^(6a)OH) as alcohol component 2, or when using a single alcohol or analcohol mixture comprising a monohydric alcohol of 1 to 5 carbon atoms(R^(5a)OH) (P) and a monohydric alcohols of 6 to 18 carbon atoms(R^(6a)OH) (Q) (wherein (P): (O) is 0.1:99.9 to 100:0 (molar ratio)) asalcohol component 1 and a single alcohol or an alcohol mixture in whichthe constituent alcohols are the same as those of alcohol component 1and which comprises a monohydric alcohol of 1 to 5 carbon atoms(R^(5a)OH) (S) and a monohydric alcohols of 6 to 18 carbon atoms(R^(6a)OH) (T) (wherein (S):(T) is 0:100 to 99.9:0.1 (molar ratio)) asalcohol component 2, esters represented by the formulas (7) and (8)given below are produced as by-products, in addition to the mixeddiester represented by the formula (4a) according to the presentinvention, but the diesters represented by the formulas (7) and (8) canbe used as a refrigerator oil as admixed with the mixed diester of theformula (4a) according to the invention:

-   1) the alicyclic or aromatic adjacent dicarboxylic acid mixed    di(lower alkyl)ester of the formula (7)    wherein A and X are as defined above, and two R s are the same and    R^(5a) is a group resulting from elimination of hydroxyl group from    the monohydric alcohol of 1 to 5 carbon atoms, i.e. a branched-chain    alkyl group having 3 to 5 carbon atoms, a straight-chain alkyl group    having 1 to 5 carbon atoms, a straight-chain alkenyl group having 2    to 5 carbon atoms or a cycloalkyl group having 3 to 5 carbon atoms,    and the two —COOR^(5a) groups are attached to two adjacent carbon    atoms of a cyclohexane ring, a cyclohexene ring or a benzene ring    represented by A;-   2) an alicyclic or aromatic adjacent dicarboxylic acid mixed diester    of the formula (4a)    wherein A and X are as defined above, R^(5a) and R^(6a) are    different from each other, and R^(5a) is as defined above, and    R^(6a) is a group resulting from elimination of hydroxyl group from    the monohydric alcohol of 6 to 18 carbon atoms, i.e. a    branched-chain alkyl group having 6 to 18 carbon atoms, a    straight-chain alkyl group having 6 to 18 carbon atoms, a    straight-chain alkenyl group having 6 to 18 carbon atoms or a    cycloalkyl group having 6 to 10 carbon atoms, and the group    —COOR^(5a) and the —COOR^(6a) group are attached to two adjacent    carbon atoms of a cyclohexane ring, a cyclohexene ring or a benzene    ring represented by A; and-   3) an alicyclic or aromatic adjacent dicarboxylic acid mixed    di(higher alkyl)ester of the formula (8)    wherein A and X are as defined above and two R^(6a)s are the same    and R^(6a) is a group resulting from elimination of a hydroxyl group    from the monohydric alcohol of 6 to 18 carbon atoms, i.e. a    branched-chain alkyl group having 6 to 18 carbon atoms, a    straight-chain alkyl group having 6 to 18 carbon atoms, a    straight-chain alkenyl group having 6 to 18 carbon atoms or a    cycloalkyl group having 6 to 10 carbon atoms; and the two —COOR^(6a)    groups are attached to two adjacent carbon atoms of a cyclohexane    ring, a cyclohexene ring or a benzene ring represented by A.

After completion of the esterification reaction, the excess startingmaterials are distilled off under reduced pressure or under atmosphericpressure. When the process is intended to prepare only the alicyclic oraromatic adjacent dicarboxylic acid mixed diester of the formula (4)(e.g. the ester of the formula (4a)), the ester mixture (e.g. an estermixture of an ester of the formula (7), an ester of the formula (4a) andan ester of the formula (8)) prepared by the foregoing process may bepurified by distillation to remove the ester of the formula (6) (e.g.the esters of the formulas (7) and (8)). In this case, it is preferableto purify the ester mixture by the method to be described below and thenseparate the ester of the formula (4a) by a known method such asdistillation.

In a preferred aspect of the invention, however, it has been found thatan ester mixture of 1) an ester of the formula (7), 2) a mixed diesterof the formula (4a) and 3) an ester of the formula (8) is useful as arefrigerator oil.

Thus, the present invention also provides a lubricating oil for arefrigerator (refrigerator oil) comprising a mixture of:

-   -   1) an ester of the formula (7),    -   2) a mixed diester of the formula (4a) and    -   3) an ester of the formula (8).

A wider range of the proportions of esters 1), 2) and 3) in the abovemixture is made available by changing the ratio of alcohol component 1and alcohol component 2 to be used or can vary by changing the reactiontemperature and reaction time in step (b). Generally, it is preferablethat mixed diester 2) is present in a proportion of 100, ester 1) ispresent in a proportion of about 5 to 300, particularly 7 to 100 andester 3) is present in a proportion of 7 to 500, preferably 10 to 350.Herein, the proportions are expressed by area ratio as determined on agas chromatogram of a mixture of esters 1), 2) and 3). The conditionsunder which gas chromatography is conducted will be described inExamples.

Purification of Ester of the Invention

In embodiment I and in embodiment II as well, after the esterificationreaction, the step of evaporating the excess starting materials(especially alcohols) from a reaction mixture under reduced pressure (at133 to 66500 Pa) or under atmospheric pressure at 100 to 230° C., andthe neutralization and water-washing step of the obtained crude esterare carried out.

The order of carrying out the excess starting material evaporation stepand the neutralization and water-washing step is not particularlylimited, but it is preferable to conduct the excess starting materialevaporation step first, followed by the neutralization and water-washingstep.

Neutralization can be carried out by various methods. For example,neutralization step is preferably carried out as follows: First, a 0.1to 10 wt. % aqueous solution of alkali (an alkali metal hydroxide suchas sodium hydroxide and potassium hydroxide, an alkali metal carbonatesuch as sodium carbonate and potassium carbonate) is added to anesterification reaction product obtained by evaporation of excessalcohol(s) after the esterification reaction or acid component andalcohol component used as the starting materials in the esterificationreaction. The amount of the aqueous solution of alkali is preferably 2to 20 parts by weight, per 100 parts by weight of said esterificationreaction product or per 100 parts by weight of a total weight of theacid component and alcohol. Then, the resulting mixture is stirred atroom temperature to 90° C. for 10 minutes to 5 hours, preferably 30minutes to 2 hours. By this neutralization, unreacted carboxylic acid(s)can be removed and the catalyst used in the reaction and organometalliccompounds derived from the catalyst are decomposed.

The step of washing the crude product with water after theneutralization is carried out until the washings (=water used for thiswashing step) are neutral, and the method of washing is not particularlylimited. For example, the water-washing step can be carried out at roomtemperature to 90° C. by using water in a total amount of 10 to 1000parts by weight per 100 parts by weight of said crude product until thewashings are neutral.

Whether the neutralization is complete or not can be confirmed bymeasuring the total acid number of the esterification reaction product(crude ester) after being washed with water. For example, theneutralization may be carried out until the total acid number of theesterification reaction product (crude ester) becomes 0.05 mgKOH/g orless, preferably about 0.02 mgKOH/g. When the esterification reactionproduct (crude ester) has a total acid number of higher than 0.05mgKOH/g, it is preferable to carry out the neutralization and washingwith water again until the total acid number of the esterificationreaction product (crude ester) becomes 0.05 mgKOH/g or less.

Then, purification step is carried out using liquid-liquid extraction ordistillation under reduced pressure or purification by adsorbents or thelike to purify the ester. In the purification step, it is recommended touse a procedure which do not allow incorporation of a sulfur elementand/or phosphorus element into the ester.

The obtained ester contains various impurities depending on theproducing process. Examples of such impurities are acidic compounds,metal compounds, hetero atom-containing compounds, oxygen-containingorganic compounds and the like. The acidic compounds include inorganicand organic acid components. The metal compounds include metals ingeneral derived from the raw materials and the catalyst. The heteroatom-containing compounds include sulfur-containing compounds,phosphorus-containing compounds, etc. The oxygen-containing organiccompounds include peroxides, carbonyl compounds and the like which wouldparticularly affect the ester. These impurities may deteriorate thehydrolysis stability, electrical insulating property and heat stabilityand may lead to corrosion of metal parts and to generation of sludge.For this reason, it is desirable to sufficiently remove the impuritiesfrom the ester in the purification step.

Among the foregoing procedures for the purification step, distillationunder reduced pressure, purification using adsorbents are particularlypreferable, and the purification using adsorbents is more preferable.

Liquid-liquid extraction can be carried out by a conventionalliquid-liquid extraction method using one or more organic solvents suchas hexane, toluene, xylene, methanol and the like.

Distillation under reduced pressure can be carried out at a temperatureof 100 to 300° C. at a reduced pressure of 13 to 13300 Pa.

The purification using adsorbents which is a more preferable procedurewill be described below in detail.

Useful adsorbents include, for example, natural or synthetic adsorbents,specifically activated carbon, activated alumina, silica gel,silica-alumina, activated clay, zeolite, magnesia, calcia, diatomaceousearth, hydrotalcite, as well as synthetic adsorbents such as ionexchange resins of the non-sulfonic acid type, synthetic hydrotalciteand the like. The amount of the adsorbent(s) to be used may verydepending on the kind thereof, but, it is recommendable to use theadsorbent(s) in an amount of 0.01 to 5 wt. %, preferably 0.05 to 5 wt.%, relative to the theoretical yield of the alicyclic or aromaticdicarboxylic acid diester of the formula (E) of the present invention.

In the purification with an adsorbent, it is advantageous to use, forexample, 1 to 4 kinds of adsorbents, particularly 2 to 4 kinds ofadsorbents in combination.

The shape of the adsorbent to be used in the present invention is notlimited, and examples thereof are powders, molded products among whichpowders are preferred.

It is recommended that the particle size of the powdery adsorbents is,for example, 0.01 to 1000 μm, preferably 0.1 to 500 μm.

When at least 2 kinds of adsorbents are used, adsorption treatment maybe performed using one adsorbent for one of operations (stepwise), orusing said at least 2 kinds of adsorbents in admixture for a singleadsorption procedure. It is recommended to use at least 2 kinds ofadsorbents in admixture for a single adsorption procedure.

The combined use of at least 2 adsorbents different in adsorptionmechanisms is more effective. For example, activated carbon effectsphysical adsorption of polar substances, and activated alumina bringsabout physical adsorption of acidic substances. Silica gel causesadsorption due to hydrogen bond between a polar substance and a silanolgroup existing on the surface of silica gel.

Examples of preferred combinations of adsorbents are as follows:

-   -   activated carbon+activated alumina,    -   activated carbon+silica gel,    -   activated carbon+magnesia,    -   activated carbon+activated clay,    -   activated carbon+silica-alumina,    -   activated alumina+activated clay,    -   activated carbon+zeolite,    -   activated carbon+hydrotalcite,    -   activated clay+zeolite.

To improve adsorption performance, the combined use of at least 3adsorbents is also effective. Examples of such combinations are asfollows.

-   -   Activated carbon+activated alumina+silica gel,    -   Activated carbon+silica gel+magnesia,    -   Activated carbon+activated clay+activated alumina,    -   Activated carbon+hydrotalcite+zeolite,    -   Activated carbon+activated clay+hydrotalcite.

When two adsorbents are used conjointly, the proportions of said twoadsorbents are not particularly limited and are variable depending onthe kind of adsorbents. Usually, it is recommended that they are used ina weight ratio of, for example, 1/100 to 100/1, preferably 1/9 to 9/1,more preferably 3/7 to 7/3.

When three or more adsorbents are used, the proportions of theseadsorbents are as follows. For example, when 3 adsorbents are used, itis recommended to use the foregoing two adsorbents and a third adsorbentwherein the weight ratio of said two adsorbents/the third adsorbent is,for example, 1/100 to 100/1, preferably 1/9 to 9/1, more preferably 3/7to 7/3.

When 4 adsorbents are used, it is recommended to use the foregoing threeadsorbents and a fourth adsorbent wherein the weight ratio of said threeadsorbents/the fourth adsorbent is, for example, 1/100 to 100/1,preferably 1/9 to 9/1, more preferably 3/7 to 7/3.

The adsorbents to be used in the invention may be dehydrated before useto enhance the adsorbing ability. For example, dehydration before use isconducted at 60° C. to 150° C. for 30 minutes to 10 hours underatmospheric pressure or under reduced pressure, preferably a reducedpressure of 133 to 66500 Pa (1-500 mmHg).

The purification method by adsorption is exemplified below.

1) 0.01 to 5 parts by weight, preferably 0.05 to 5 parts by weight oftwo or more adsorbents are added to 100 parts by weight of thedicarboxylic acid diester prepared by the foregoing process ofembodiment I or embodiment II and subjected to the neutralization andwater-washing steps. The mixture is stirred with heating at 70 to 120°C., preferably 80° C. to 110° C. for 10 minutes to 2 hours, preferably30 minutes to 1 hour, under atmospheric pressure or reduced pressure(e.g. 133 to 66500 Pa (1-500 mmHg)). In this procedure, an adsorptioncolumn charged with adsorbents may be used, and the adsorption treatmentis carried out by passing the ester through the column.

2) The ester prepared by the foregoing process is treated according tothe above-mentioned method 1) using one adsorbent, followed by furtheradsorption treatment with another adsorbent. Optionally two or moreadsorption columns may be set in series and individually charged with anadsorbent, and the alicyclic dicarboxylic acid diester is passed throughthe columns one by one for adsorption treatment.

Herein, it is recommended that an aqueous solution of an alkali, water,organic solvents, adsorbents and the like to be used in thewater-washing step, neutralization step and purification step should becompletely or substantially free of a sulfur element and/or a phosphoruselement.

It is recommended that the alicyclic dicarboxylic acid diesterrepresented by the formula (1) and the alicyclic or aromatic adjacentdicarboxylic acid mixed diester represented by the formula (4), as wellas refrigerator lubricating oil comprising one or more of these estershave a water content of 100 ppm or less, preferably 50 ppm or less.Therefore, it is preferable to remove water by sufficiently carrying outdehydration treatment. The dehydration may be carried out, for example,under atmospheric or reduced pressure, preferably under a reducedpressure of 133 Pa to 66500 Pa, at a temperature ranging from roomtemperature to 150° C., preferably 50 to 140° C., for 0.1 hour to 10hours. If the water content exceeds 100 ppm, hydrolysis might possiblytake place, thereby affecting electrical insulation properties, heatstability and hydrolysis stability.

When the foregoing purification step and the dehydration step arecarried out, the order thereof is not particularly limited. However,there is a possibility that the ester may absorb water during thepurification step, and therefore it is preferable to carry outdehydration step after the purification step.

A preferred method for preparing the alicyclic or aromatic dicarboxylicacid diester represented by the formula (E) according to the presentinvention recommendably comprises the steps of

-   (i) carrying out the esterification reactions by the method of    embodiment I or II to obtain an ester mixture,-   (ii) removing excess starting materials (especially alcohol(s)) from    the ester obtained in step (i),-   (iii) neutralizing the crude ester obtained in step (ii) and washing    the neutralized crude ester with water,-   (iv) purifying the crude ester neutralized and washed with water in    step (iii) by treatment with 1 to 4 kinds of adsorbents,-   (v) dehydrating the purified ester obtained in step (iv).

The alicyclic or aromatic dicarboxylic acid diesters represented by theformula (E), particularly, the alicyclic or aromatic dicarboxylic aciddiesters represented by formula (4) or the ester mixture (such as aester mixture of the ester represented by the formula (7), the esterrepresented by the formula (4a) and the ester represented by the formula(8)) prepared by the process of embodiment I or embodiment II andpurified by the above purification method comprising the steps (i) to(v) above have the following properties and is suitable as arefrigerator oil:

-   -   1) a total acid number of 0.05 mgKOH/g or less, preferably 0.02        mgKOH/g or less. The term “total acid number” used herein refers        to a value prescribed in JIS-K-2501, and more specifically means        the number of milligrams of potassium hydroxide required to        neutralize the total acid components contained in 1 g of the        sample. The higher the number is, the more the amount of the        acid components in the sample is,    -   2) a sulfated ash content of 10 ppm or less, preferably 5 ppm or        less (as measured according to JIS-K-2272.5),    -   3) a sulfur content of 20 ppm or less, preferably 10 ppm or        less. The sulfur content is measured by diluting 5.0 g of a        sample ester with hexane to give a 10.0 ml dilution and the        sulfur content of the ester is measured with a sulfur analyzer        TS-03 (product of Mitsubishi Chemical Corp.)),    -   4) a phosphorus content of 20 ppm or less, preferably 10 ppm or        less (as measured according to JIS-K-0102-1998),    -   5) a hydroxyl value of 3 mgKOH/g or less, preferably 2 mgKOH/g        or less (as measured according to JIS-K-0070),    -   6) a peroxide value of 1.0 meq/kg or less, preferably 0.5 meq/kg        or less (as measured according to 2.5.2-1996 of Standard Methods        for the Analysis of Fats, Oil and Related Materials (Japan Oil        Chemists' Society)),    -   7) a carbonyl value of 10 or less, preferably 5 or less (as        measured according to 2.5.4-1996 of Standard Methods for the        Analysis of Fats, Oil and Related Materials (Japan Oil Chemists'        Society)),    -   8) a volume resistivity of 1×10¹¹ Ω·cm or more, preferably        1×10¹² Ω·cm or more (as measured at 25° C. according to        JIS-C-2101), and    -   9) a water content of 100 ppm or less, preferably 50 ppm or less        (as measured according to JIS-K-2275 using Karl Fischer's        moisture meter).

The ester represented by the formula (1) according to embodiment Iadditionally has:

-   10) a hue of 50 or less, preferably 30 or less (Hasen color number    as measured according to JIS-K-0071-1-1998).

When the alicyclic dicarboxylic acid diester has the above-mentionedproperties outside of said respective ranges, the ester is inferior inelectrical insulating property, heat stability and hydrolysis stability.

Specifically,

-   1) When the total acid number exceeds 0.05 mgKOH/g, the ester tends    to be inferior in hydrolysis stability and becomes more corrosive to    metals,-   2) When sulfated ash content exceeds 10 ppm, the ester tends to be    inferior in heat stability, electrical insulating property.-   3) When sulfur content exceeds 20 ppm, the ester tends to be    inferior in heat stability, hydrolysis stability and electrical    insulating property.-   4) When phosphorus content exceeds 20 ppm, the ester tends to be    inferior in heat stability, hydrolysis stability and electrical    insulating property.-   5) When hydroxyl value exceeds 3 mgKOH/g, the ester is more    hygroscopic and tends to be inferior in hydrolysis stability and    electrical insulating property.-   6) When peroxide value exceeds 1.0 meq/kg, the ester tends to be    inferior in heat stability and electrical insulating property.-   7) When carbonyl value exceeds 10, the ester tends to be inferior in    heat stability and electrical insulating property.-   8) When volume resistivity is less than 1×10¹¹ Q-cm, the ester tends    to be inferior in electrical insulating property.-   9) When water content exceeds 100 ppm, the ester tends to be    inferior in electrical insulating property, heat stability and    hydrolysis stability.

Lubricating Oil for a Refrigerator

The lubricating oil for a refrigerator (refrigerator oil) according tothe present invention contains either the alicyclic dicarboxylic aciddiester of the formula (1) prepared by the process of embodiment I orthe alicyclic or aromatic dicarboxylic acid mixed diester of the formula(4) prepared by the process of embodiment II.

In other words, the ester or a mixture of the esters according toembodiment I and II of the invention can be used as a refrigerator oil.

The amount of the alicyclic dicarboxylic acid diester of the formula (1)according to embodiment I in a refrigerator oil is not limited but ispreferably 10 wt. % or more, more preferably 20 wt. % or more, based onthe total amount of refrigerator oil.

The amount of the alicyclic or aromatic adjacent dicarboxylic acid mixeddiester of the formula (4) in a refrigerator oil is not limited, but ispreferably 10 wt. % or more, more preferably 20 wt. % or more, based onthe total amount of refrigerator oil.

Particularly, the refrigerator oil of the invention preferably contains

-   -   1) an alicyclic or aromatic adjacent dicarboxylic acid mixed        diester of the formula (4) and    -   2) an alicyclic or aromatic adjacent dicarboxylic acid diester        of the formula (6).

The mixing ratio of the alicyclic or aromatic adjacent dicarboxylic acidmixed diester (A) of the formula (4) and the alicyclic or aromaticadjacent dicarboxylic acid diester (B) of the formula (6) isrecommendably 10 to 800 parts by weight, preferably 17 to 450 parts byweight, of (B), per 100 parts by weight of (A).

Particularly, the present invention also provides a refrigeratorlubricating oil (refrigerator oil) comprising an ester mixture of:

-   -   1) the ester of the formula (7),    -   2) the mixed diester of the formula (4a) and    -   3) the ester of the formula (8).

A wider range of the proportions of esters 1), 2) and 3) in the abovemixture is made available by changing the ratio of alcohol component 1and alcohol component 2 or can vary by changing the reaction temperatureand reaction time in step (b). Generally, it is preferable that mixeddiester 2) is present in a proportion of 100, ester 1) is present in aproportion of about 5 to 300, particularly about 7 to 100 and ester 3)is present in a proportion of about 7 to 500, preferably about 10 to350. Herein, the proportions are expressed by area ratio as determinedon a gas chromatogram of a mixture of esters 1), 2) and 3). Theconditions under which gas chromatography is conducted will be describedin Examples.

The refrigerator oil according to the invention may further contain oneor more compounds selected from other lubricating oil base stock(hereinafter referred to as “concomitant base stock”) within the rangewhich does not affect the effects of the invention.

Examples of the concomitant base stock are one or more compoundsselected from the group consisting of mineral oil (hydrocarbon oilobtained by petroleum refining), poly-α-olefins, polybutenes,alkylbenzenes, alkylnaphthalenes and like synthetic hydrocarbons,isomerized oil of synthetic hydrocarbon prepared by the Fischer-Tropschprocess, organic acid esters, polyalkylene glycols, polyvinyl ethers,polyphenyl ethers, alkylphenyl ethers and silicone oils.

Examples of the mineral oil include solvent-refined mineral oils,hydrogenated refined mineral oils, wax-isomerized oils, etc. Usually itis recommended to use mineral oils having a kinematic viscosity of 1.0to 40 mm²/s, preferably 2.0 to 30 mm²/s, at 100° C.

Examples of the poly-α-olefin include polymers or copolymers ofalpha-olefin(s) of 2 to 16 carbon atoms (such as ethylene, propylene,1-butene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene,1-hexadecene, etc.) having a kinematic viscosity of 1.0 to 40 mm²/s at100° C. and a viscosity index of 100 or more, among which recommendableare those having a kinematic viscosity of 2.0 to 30 mm²/s at 100° C. anda viscosity index of 120 or more.

Examples of the polybutene include polymers prepared by polymerizationof isobutylene or by copolymerization of isobutylene and normal butyleneand having a kinematic viscosity in a wide range of 2.0 to 6000 mm²/s at100° C.

Examples of the alkylbenzene include monoalkyl-benzenes,dialkylbenzenes, trialkylbenzenes, tetraalkylbenzenes, etc. in which thealkyl substituent(s) is(are) a straight-chain or branched-chain alkylgroup having 1 to 40 carbon atoms, and which have a molecular weight of200 to 450.

Examples of the alkylnaphthalene include monoalkylnaphthalene,dialkylnaphthalene, etc. in which the alkyl substituent(s) is(are) astraight-chain or branched-chain alkyl group having 1 to 30 carbonatoms.

Examples of the organic acid ester other than the present ester includealiphatic dibasic acid esters, aromatic polycarboxylic acid esters(other than phthalic acid mixed diesters), polyol esters and otheresters.

Examples of the aliphatic dibasic acid esters include aliphatic dibasicacid diesters prepared from an aliphatic dicarboxylic acid of 6 to 12carbon atoms such as adipic acid, azelaic acid, sebacic acid,dodecane-diacid or the like with a straight-chain or branched-chainsaturated or unsaturated aliphatic alcohol of 3 to 22 carbon atoms.

Examples of the aromatic polycarboxylic acid esters are esters of anaromatic polycarboxylic acid such as isophthalic acid, terephthalicacid, trimellitic acid, pyromellitic acid or the like or anhydridethereof with a straight-chain or branched-chain saturated or unsaturatedaliphatic alcohol of 3 to 22 carbon atoms.

Examples of the polyol esters include esters of a polyol such asneopentyl glycol, trimethylolpropane, pentaerythritol,ditrimethylolpropane, dipentaerythritol or the like with astraight-chain and/or branched-chain saturated fatty acid of 3 to 22carbon atoms.

Examples of other esters are carboxylic acid esters such as esters ofdimer acid or a hydrogenation product thereof (saturated acid) with astraight-chain or branched-chain saturated or unsaturated aliphaticalcohol of 3 to 22 carbon atoms, aliphatic branched-chain carboxylicacid monoalkyl ester, aliphatic straight-chain carboxylic acid monoalkylester, etc.

Useful polyalkylene glycols include, for example, those prepared by ringopening polymerization of a straight-chain or branched-chain alkyleneoxide of 2 to 4 carbon atoms with an alcohol. Examples of the alkyleneoxide are ethylene oxide, propylene oxide, butylene oxide and the like.Polymers prepared from one of them, and copolymers prepared from amixture of at least two of them can be used. Further it is possible touse compounds having a hydroxyl moiety etherified or esterified in oneor both ends of the molecule. Useful polyalkylene glycols arerecommendably those having a kinematic viscosity of preferably 5.0 to1000 mm²/s (40° C.), more preferably 5.0 to 500 mm²/s (40° C.).

Examples of the polyvinyl ethers include compounds prepared bypolymerization of vinyl ether monomer, and examples of the monomer aremethyl vinyl ether, ethyl vinyl ether, isopropyl vinyl ether, n-butylvinyl ether, isobutyl vinyl ether, sec-butyl vinyl ether, tert-butylvinyl ether, n-pentyl vinyl ether, n-hexyl vinyl ether, 2-methoxyethylvinyl ether, 2-ethoxyethyl vinyl ether and the like. Useful polyvinylethers are recommendably those having a kinematic viscosity ofpreferably 5.0 to 1000 mm²/s (40° C.), more preferably 5.0 to 800 mm²/s(40° C.).

Examples of the polyphenyl ether include compounds having a structurewherein at least 2 meta-positions on the aromatic ring are bonded byether linkage or thioether linkage. More specific examples thereof arebis(m-phenoxyphenyl)ether, m-bis(m-phenoxyphenoxy)benzene and the like.

Useful alkyl phenyl ethers include, for example, compounds having astraight-chain or branched-chain alkyl group of 6 to 18 carbon atoms assubstituent(s), and particularly preferred examples thereof includealkyldiphenyl ether having one or two alkyl groups as substituent(s).

Examples of silicone oils include dimethyl silicone, methylphenylsilicone, long chain alkyl silicone, fluorosilicone and like modifiedsilicones.

When the concomitant base stock is used, the amount of the concomitantbase stock in the refrigerator oil of the invention is 10 to 90 wt. %,recommendably 10 to 50 wt. %.

When the alicyclic dicarboxylic acid diester according to embodiment Ior the alicyclic or aromatic adjacent dicarboxylic acid mixed diesteraccording to embodiment II of the present invention is used in arefrigerator oil, one or more additives such as antioxidants, metaldeactivator, defoaming agents, hydrolysis depressants and the like mayoptionally be added to improve the performance of esters. There is nolimitation on such additives insofar as they can achieve the desiredeffects. Specific examples of such additives are described below.

Examples of useful antioxidants are 2,6-di-tert-butyl-p-cresol,4,4′-methylenebis-2,6-di-tert-butylphenol and like phenols,N-phenyl-α-naphthylamine, p,p′-dioctyldiphenylamine and like amines. Theantioxidant, if used, may be added usually in an amount of 0.01 to 5 wt.%, preferably 0.1 to 2 wt. %, based on the refrigerator oil.

Examples of metal deactivator are benzotriazole compounds and likecompounds. The metal deactivator, if used, may be added in an amount of0.01 to 0.4 wt. % based n the refrigerator oil.

A liquid silicone is suitable for use as a defoaming gent. The defoamingagent, if used, may be added in an amount of 0.0005 wt. % to 0.01 wt. %based on the refrigerator oil.

Examples of useful hydrolysis depressants are epoxy compounds such asalkyl glycidyl ethers, phenyl glycidyl ethers, alkyleneglycol glycidylethers, glycidyl esters, alicyclic epoxy compounds, epoxidized alkeneand derivatives thereof. The hydrolysis depressant, if used, may beadded in an amount of 0.05 wt. % to 2 wt. % based on the refrigeratoroil.

Processes for preparing the refrigerator oil of the invention include,for example, a process comprising the steps of adding the alicyclicdicarboxylic acid diester of the formula (1) according to embodiment Ior the alicyclic or aromatic adjacent dicarboxylic acid mixed diester ofthe formula (4) or the ester mixture containing the mixed diester (suchas the ester mixture of the ester of the formula (7), the ester of theformula (4a) and the ester of the formula (8)) according to embodimentII and if desired said one or more concomitant base stocks and/or saidone or more additives, and uniformly dissolving them. There is nolimitation on the order of adding the concomitant base stock andadditives. Dehydration may be conducted after uniform dissolution forcontrol of water.

Depending on the kind of refrigerator to be used, the alicyclicdicarboxylic acid diester of the formula (1) according to embodiment Ialone or the alicyclic or aromatic adjacent dicarboxylic acid mixeddiester or an ester mixture containing the mixed diester according toembodiment II may be used as a refrigerator oil.

The refrigerator oil of the present invention can be used as alubricating oil for a variety of refrigerators in whichhydrofluorocarbon is used as a refrigerant. Examples of suchhydrofluorocarbons are HFC-134a, HFC-134, HFC-125, HFC-32, HFC-143a, andmixed refrigerants thereof such as R404A, R407A, R407C, R407E, R410A,R507A, etc.

The following effects can be achieved by using, as a refrigerator oil,the alicyclic dicarboxylic acid diester of the formula (1) preparedaccording to embodiment I of the present invention.

1) The alicyclic dicarboxylic acid diester prepared using an aliphaticmonohydric alcohol having a peroxide value adjusted to not more than 1.0meq/kg is advantageous in respect of hue, peroxide value, etc. andexcellent in electrical insulating property, heat stability, long-termhydrolysis stability, etc.

2) The alicyclic dicarboxylic acid diester prepared using an aliphaticmonohydric alcohol having a peroxide value of not more than 1.0 meq/kgand having a carbonyl value of 15 or less can exhibit more improvedproperties in respect of hue, peroxide value, heat stability andlong-term hydrolysis stability.

3) The alicyclic dicarboxylic acid diester prepared by esterificationreaction in the absence of a catalyst or in the presence of asulfur-free and phosphorus-free catalyst has a volume resistivity of1.0×10¹¹ Ω·cm or more and involves only a small degree of increase inacid number by heating, and thus shows a high heat stability and alsooutstanding long-term hydrolysis stability.

The mixed diester prepared by the 2-step esterification processaccording to embodiment II of the invention, when used as a refrigeratoroil, produces the following effects.

1) Said mixed diester can be prepared under milder conditions than themixed diester prepared by the 1-step esterification process, and is ofhigh quality. This ester, when used as a refrigerator oil, displays ahigh hydrolysis stability, a high heat stability and an excellentelectrical insulating property. For example, the alicyclic adjacentdicarboxylic acid mixed diester prepared by the 1-step esterificationprocess or the ester prepared by the 2-step esterification process inthe presence of a sulfur-containing catalyst is insufficient inhydrolysis stability and heat stability, whereas the ester prepared bythe 2-step esterification process according to the present invention ismuch improved in hydrolysis stability, heat stability and electricalinsulating property.

2) By suitably changing the kinds and/or mixing ratio of alcohols inalcohol component 1 and alcohol component 2 used for esterification, thedesired mixed diester can be prepared which can satisfy the need forvarious viscosity characteristics.

3) In preparing the mixed diester according to the 2-step esterificationreaction, the use of aliphatic monohydric alcohol(s) having a peroxidevalue of 1.0 meq/kg or less and further having a carbonyl value of 15 orless gives the desired mixed diester which is still more advantageouswith respect to peroxide value, heat stability and hydrolysis stability.

It is known that a refrigeration system is exposed to a pronouncedlyhigh temperature due to friction during the operation of a compressor ina refrigerator. In view of this condition, it is important for therefrigerator oil to have a high heat stability and to exhibit a highstability during exposure to a high temperature. The electricalinsulating property is also important to prevent an accident due toleakage during the operation of a refrigerator. After the ester isexposed to a high temperature, the smaller the increase of total acidnumber is, the higher the heat stability is. The higher the volumeresistivity of the ester is, the higher the electrical insulatingproperty is.

Examples of refrigerators for which the refrigerator oil of theinvention can be used are compressors in automotive air conditioners,refrigerators, automatic vending machines, refrigeration-type displaycases, room air conditioners or large-size refrigerators for industrialuse or the like in which hydrofluorocarbon is used as a refrigerant.

EXAMPLES

Embodiment I of the present invention will be described in greaterdetail with reference to the following examples and comparativeexamples. The properties of lubricating oils prepared in these examplesand the like were evaluated by the following methods.

Kinematic Viscosity

Measured according to JIS-K-2283 using Ubbellohde viscometer.

Total Acid Number

Measured according to JIS-K-2501.

Hue

Hazen color number was measured according to JIS-K-0071-1-1998.

Sulfated Ash Content

Measured according to JIS-K-2272.5

Sulfur Content

A sample ester (5.0 g) was diluted with hexane to give a 10.0 mldilution, and the sulfur content of the ester was measured with a sulfuranalyzer, TS-03 (product of Mitsubishi Chemical Corp.)

Phosphorus Content

Measured according to JIS-K-0102-1998.

Hydroxyl Value

Measured according to JIS-K-0070.

Peroxide Value

Measured according to 2.5.2-1996 of Standard Methods for the Analysis ofFats, Oil and Related Materials (Japan Oil Chemists' Society)

Carbonyl Value

Measured according to 2.5.4-1996 of Standard Methods for the Analysis ofFats, Oil and Related Materials (Japan Oil Chemists' Society)

Test for Electrical Insulating Property

The volume resistivity was measured at 25° C. according to JIS-C-2101.The higher the volume resistivity is, the more excellent the electricalinsulating property is.

Test for Heat Stability

Iron wire, copper wire and aluminum wire, 1.6 mm in diameter and 40 mmin length, were placed in a beaker of 53 mm in inner diameter and 56 mmin height. 40 g of an ester sample was weighed out and introduced intothe beaker. The beaker was placed in an oven and was heated at 175° C.for 15 hours. Then the ester sample was taken out to measure the totalacid number. The smaller the increase in total acid number after thetest as compared with that before the test is, the higher the heatstability is. The result obtained in this test is an index of resistanceof the ester to oxidative deterioration.

Test for Hydrolysis Stability

Iron wire, copper wire and aluminum wire of 1.6 mm in diameter and 40 mmin length were placed in a glass test tube of 6.6 mm in inner diameterand 30 cm in height. Then, 2.0 g of an ester sample and 0.2 g ofdistilled water were weighed out and introduced into the test tube. Thetest tube was sealed while it was degassed by an aspirator. The testtube was placed into an oven and was heated at 175° C. for 80 hours.Then the ester sample was taken out to measure the total acid number. Itis considered that the smaller the increase in total acid number is, thehigher the hydrolysis stability is. The result obtained in this test isan index of hydrolysis resistance of the ester as heated in the presenceof water.

Water Content

Measured according to JIS-K-2275 using Karl Fischer's moisture meter(MKC-510, product of Kyoto Denshi Kabushiki Kaisha)

Example I-1

A 4-necked flask equipped with a stirrer, a thermometer and a Dean-Starkwater separator was charged with 152.1 g (1 mole) of4-cyclohexene-1,2-dicarboxylic anhydride (prepared by usual Diels-Alderreaction of maleic anhydride with 1,3-butadiene), 162.8 g (2.2 moles) ofisobutanol having a peroxide value of 0.2 meq/kg and a carbonyl value of0.3 and xylene (5 wt. % relative to the starting materials fed). Then,the mixture was gradually heated to 220° C. in the presence of tinhydroxide catalyst (0.2 wt. % based on the starting materials fed) in anitrogen atmosphere. While water generated during the reaction wasremoved by means of the water separator, the esterification reaction wasconducted at 220° C. for 15 hours until the total acid number of thereaction mixture became 2 mgKOH/g or less. Thereafter, the reaction wascontinued at 220° C. under reduced pressure (20000 Pa) for about 6hours.

After the reaction, the excess isobutanol was removed by distillation at180° C. under a reduced pressure of 1330 Pa, and the obtained liquidresidue was neutralized by adding 22 g of a 4% aqueous solution ofsodium hydroxide and stirring the mixture at 80° C. for 2 hours, andthen washed with water until the aqueous layer became neutral (totalamount of water used: about 2000 ml) to thereby give a liquid crudeester. At this point, the crude ester had a total acid number of 0.02mgKOH/g. Subsequently, to the ester was added activated alumina(“Tomita-AD 220P” manufactured by Tomita Pharmaceutical Co., Ltd.; 0.2wt. % based on the starting materials fed, namely 0.22 wt. % relative tothe theoretical yield of the ester), and the mixture was stirred at 90°C. and at 1330 Pa for 1 hour, and the activated alumina was filteredoff, whereby 269 g of purified diisobutyl4-cyclohexene-1,2-dicarboxylate was obtained. Dehydration was carriedout at 100° C. under a reduced pressure of 1330 Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained ester areshown in Table 1. The ester had a hue of 10 in terms of Hazen colornumber, a water content of 16 ppm, a sulfated ash content of 1 ppm, asulfur content of less than 1 ppm, a phosphorus content of less than 1ppm, a hydroxyl value of 0.2 mgKOH/g, a peroxide value of 0.3 meq/kg anda carbonyl value of 0.8.

Example I-2

The same procedure as in Example I-1 was carried out with the exceptionof using 286 g (2.2 moles) of 2-ethylhexanol having a peroxide value of0.1 meq/kg and a carbonyl value of 0.2 and tin oxide as a catalyst (0.2wt. % based on the starting materials fed) and conducting anesterification reaction at 230° C. for 4 hours and at 230° C. underreduced pressure (20000 Pa) for 1 hour.

Then the purification procedure of Example I-1 was followed with theexception of removing excess 2-ethylhexanol by distillation at 210° C.under a reduced pressure of 1330 Pa, whereby 376 g of purifieddi(2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate was produced.Dehydration was carried out at 130° C. under a reduced pressure of 1330Pa for 5 hours.

The total acid number and kinematic viscosity of the obtained ester areshown in Table 1. The ester had a hue of 10 in terms of Hazen colornumber, a water content of 12 ppm, a sulfated ash content of less than 1ppm, a sulfur content of less than 1 ppm, a phosphorus content of lessthan 1 ppm, a hydroxyl value of 0.8 mgKOH/g, a peroxide value of 0.2meq/kg and a carbonyl value of 0.5.

Example I-3

Following the procedure of Example I-1, 152.1 g (1 mole) of4-cyclohexene-1,2-dicarboxylic anhydride and 316.8 g (2.2 moles) ofisononanol (“Oxocol 900”, product of Kyowa Hakko Kogyo Co., Ltd.) havinga peroxide value of 0.1 meq/kg and a carbonyl value of 3.0 were fed, andthe mixture was gradually heated to 200° C. in the presence oftetraisopropyl titanate catalyst (0.2 wt. % based on the startingmaterials fed) under a nitrogen atmosphere. While the generated waterwas removed by water separator, esterification reaction was conducted at200° C. for 7 hours, and at 200° C. under reduced pressure (20000 Pa)for 2 hours.

After the reaction, the excess isononanol was removed by distillation at210° C. under a reduced pressure of 1330 Pa, and the obtained liquidresidue was neutralized by adding thereto 33 g of a 4% aqueous solutionof sodium hydroxide and stirring the mixture at 80° C. for 2 hours, andthen washed with water until it became neutral. At this point, the crudeester had a total acid number of 0.02 mgKOH/g. Subsequently, to theester was added activated clay (“Galleon-earth V₁” manufactured byMizusawa Industrial Chemicals Ltd.; 0.2 wt. % based on the startingmaterials fed), and the mixture was stirred at 90° C. and at 1330 Pa for1 hour and filtered, whereby 399 g of purified diisononyl4-cyclohexene-1,2-dicarboxylate was obtained. Dehydration was carriedout at 130° C. under a reduced pressure of 1330 Pa for 5 hours.

The total acid number and kinematic viscosity of the obtained ester areshown in Table 1. The ester had a hue of 10 in terms of Hazen colornumber, a water content of 20 ppm, a sulfated ash content of less than 1ppm, a sulfur content of less than 1 ppm, a phosphorus content of lessthan 1 ppm, a hydroxyl value of 0.8 mgKOH/g, a peroxide value of 0.2meq/kg and a carbonyl value of 1.2.

Example I-4

When 3,5,5-trimethylhexanol was stored at room temperature (for oneyear), it showed a peroxide value of 0.8 meq/kg and a carbonyl value of17.2. To the 3,5,5-trimethylhexanol was added 70 ppm of sodiumborohydride, and the mixture was stirred at 80° C. for 2 hours in anitrogen atmosphere, followed by washing with water and dehydration.Filtration gave 3,5,5-trimethylhexanol having a peroxide value of 0.4meq/kg and a carbonyl value of 0.3.

The same procedure as in Example I-3 was repeated with the exception ofusing the foregoing 3,5,5-trimethylhexanol and activated carbon (0.2 wt.% based on the starting materials used) after neutralization and washingwith water, whereby purified di(3,5,5-trimethylhexyl)4-cyclohexene-1,2-dicarboxylate was produced. Then dehydration wascarried out at 130° C. under a reduced pressure of 1330 Pa for 5 hours.

The total acid number and kinematic viscosity of the obtained ester areshown in Table 1. The ester had a hue of 10 in terms of Hazen colornumber, a water content of 12 ppm, a sulfated ash content of 1 ppm, asulfur content of less than 1 ppm, a phosphorus content of less than 1ppm, a hydroxyl value of 1.1 mgKOH/g, a peroxide value of 0.6 meq/kg anda carbonyl value of 0.9.

Example I-5

When isodecanol was stored at room temperature for 8 months, it showed aperoxide value of 1.3 meq/kg and a carbonyl value of 10.7. To theisodecanol was added 70 ppm of sodium borohydride, and the mixture wasstirred at 80° C. for 1 hour in a nitrogen atmosphere, followed bywashing with water and dehydration. Filtration gave isodecanol having aperoxide value of 0.8 meq/kg and a carbonyl value of 0.5.

The same procedure as in Example I-2 was repeated with the exception ofusing the foregoing isodecanol, whereby purified diisodecyl4-cyclohexene-1,2-dicarboxylate was produced. Then dehydration wascarried out at 130° C. under a reduced pressure of 1330 Pa for 5 hours.The total acid number and kinematic viscosity of the obtained ester areshown in Table 1. The ester had a hue of 20 in terms of Hazen colornumber, a water content of 25 ppm, a sulfated ash content of 1 ppm, asulfur content of less than 1 ppm, a phosphorus content of less than 1ppm, a hydroxyl value of 0.2 mgKOH/g, a peroxide value of 0.6 meq/kg anda carbonyl value of 1.2.

Example I-6

Purified diisobutyl 1,2-cyclohexanedicarboxylate was produced followingthe procedure of Example I-1 with the exception of using isobutanolhaving a peroxide value of 0.2 meq/kg and a carbonyl value of 0.3 and1,2-cyclohexanedicarboxylic anhydride (prepared by hydrogenating4-cyclohexene-1,2-dicarboxylic anhydride obtained by usual Diels-Alderreaction of maleic anhydride and 1,3-butadiene). Subsequentlydehydration was carried out at 100° C. under a reduced pressure of 1330Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained ester areshown in Table 1. The ester had a hue of 10 in terms of Hazen colornumber, a water content of 23 ppm, a sulfated ash content of less than 1ppm, a sulfur content of less than 1 ppm, a phosphorus content of lessthan 1 ppm, a hydroxyl value of 0.1 mgKOH/g, a peroxide value of 0.2meq/kg and a carbonyl value of 0.1.

Example I-7

Purified di(2-ethylhexyl) 1,2-cyclohexanedicarboxylate was produced bythe same procedure as in Example I-2 with the exception of using2-ethylhexanol having a peroxide value of 0.1 meq/kg and a carbonylvalue of 0.2 and 1,2-cyclohexanedicarboxylic anhydride (prepared byhydrogenating 4-cyclohexene-1,2-dicarboxylic anhydride obtained by usualDiels-Alder reaction of maleic anhydride and 1,3-butadiene).Subsequently dehydration was carried out at 130° C. under a reducedpressure of 1330 Pa for 5 hours.

The total acid number and kinematic viscosity of the obtained ester areshown in Table 1. The ester had a hue of 10 in terms of Hazen colornumber, a water content of 10 ppm, a sulfated ash content of 1 ppm, asulfur content of less than 1 ppm, a phosphorus content of less than 1ppm, a hydroxyl value of 0.3 mgKOH/g, a peroxide value of 0.3 meq/kg anda carbonyl value of 0.6.

Example I-8

Purified di(3,5,5-trimethylhexyl) 1,2-cyclohexanedicarboxylate wasproduced by the same procedure as in Example I-7 with the exception ofusing 3,5,5-trimethylhexanol having a peroxide value of 0.4 meq/kg and acarbonyl value of 0.3 (the same as used in Example I-4). Subsequentlydehydration was carried out at 130° C. under a reduced pressure of 1330Pa for 5 hours.

The total acid number and kinematic viscosity of the obtained ester areshown in Table 1. The ester had a hue of 10 in terms of Hazen colornumber, a water content of 28 ppm, a sulfated ash content of less than 1ppm, a sulfur content of less than 1 ppm, a phosphorus content of lessthan 1 ppm, a hydroxyl value of 0.9 mgKOH/g, a peroxide value of 0.5meq/kg and a carbonyl value of 0.2.

Example I-9

When 3,5,5-trimethylhexanol was stored at room temperature for one year,it showed a peroxide value of 0.8 meq/kg and a carbonyl value of 17.2.The same procedure as in Example I-8 was performed with the exception ofusing said 3,5,5-trimethylhexanol, thereby producing purifieddi(3,5,5-trimethylhexyl) 1,2-cyclohexanedicarboxylate. Then dehydrationwas carried out at 130° C. under reduced pressure of 1330 Pa for 5hours.

The total acid number and kinematic viscosity of the obtained ester areshown in Table 1. The ester had a hue of 30 in terms of Hazen colornumber, a water content of 23 ppm, a sulfated ash content of 4 ppm, asulfur content of less than 1 ppm, a phosphorus content of less than 1ppm, a hydroxyl value of 1.2 mgKOH/g, a peroxide value of 1.0 meq/kg anda carbonyl value of 9.8.

Example I-10

When 3,5,5-trimethylhexanol was stored at room temperature for one year,it showed a peroxide value of 0.8 meq/kg and a carbonyl value of 17.2.Following the procedure of Example I-8 and using the3,5,5-trimethylhexanol, the starting materials were gradually heated to225° C. in the presence of tin oxide catalyst (0.2 wt. % based on thestarting materials fed) in a nitrogen atmosphere. While water generatedduring the reaction was removed by means of water separator, theesterification reaction was conducted for 6 hours and at 225° C. underreduced pressure (20000 Pa) for 2 hours.

After the reaction, excess 3,5,5-trimethylhexanol was removed bydistillation at 210° C. under a reduced pressure of 1330 Pa, and theobtained liquid residue was neutralized by adding thereto 33 g of a 4%aqueous solution of sodium hydroxide and stirring the mixture at 80° C.for 2 hours, and then washed with water until the aqueous layer becameneutral to thereby give a liquid crude ester. At this point, the crudeester had a total acid number of 0.01 mgKOH/g. Subsequently, to theester was added activated alumina (“Tomita-AD 220P” manufactured byTomita Pharmaceutical Co., Ltd.; 0.2 wt. % based on the startingmaterials fed) and activated clay (“Galleon-earth V₁” manufactured byMizusawa Industrial Chemicals Ltd.; 0.2 wt. % based on the startingmaterials fed), and the mixture was stirred at 90° C. and at 1330 Pa for1 hour and filtered, whereby 390 g of purified di(3,5,5-trimethylhexyl)4-cyclohexene-1,2-dicarboxylate was obtained. Dehydration was carriedout at 130° C. under a reduced pressure of 1330 Pa for 5 hours.

The total acid number and kinematic viscosity of the obtained ester areshown in Table 1. The ester had a hue of 30 in terms of Hazen colornumber, a water content of 16 ppm, a sulfated ash content of less than 1ppm, a sulfur content of less than 1 ppm, a phosphorus content of lessthan 1 ppm, a hydroxyl value of 0.7 mgKOH/g, a peroxide value of 0.6meq/kg and a carbonyl value of 4.8. TABLE 1 Properties of estersKinematic Total acid viscosity number (mm²/s) Example Ester name(mgKOH/g) 40° C. 100° C. I-1 Diisobutyl 4-cyclohexene-1,2- 0.01 8.2 2.0dicarboxylate I-2 Di(2-ethylhexyl) 4-cyclohexene-1,2- 0.01 17.4 3.3dicarboxylate I-3 Diisononyl 4-cyclohexene-1,2- 0.01 21.0 4.0dicarboxylate I-4 Di(3,5,5-trimethylhexyl) 4-cyclohexene- 0.01 29.2 4.81,2-dicarboxylate I-5 Diisodecyl 4-cyclohexene-1,2- 0.01 29.4 4.7dicarboxylate I-6 Diisobutyl 1,2-cyclohexanedicarboxylate 0.01 8.0 2.0I-7 Di(2-ethylhexyl) 1,2-cyclohexane- 0.01 18.4 3.4 dicarboxylate I-8Di(3,5,5-trimethylhexyl) 1,2- 0.01 29.9 4.8 cyclohexanedicarboxylate I-9Di(3,5,5-trimethylhexyl) 1,2- 0.01 29.3 4.8 cyclohexanedicarboxylate I-10 Di(3,5,5-trimethylhexyl) 1,2- 0.01 29.3 4.8cyclohexanedicarboxylate

Comparative Example I-1

When isobutanol was stored at room temperature for 10 months, it showeda peroxide value of 1.3 meq/kg and a carbonyl value of 18.1. The sameapparatus as used in Example I-1 was charged with 162.8 g (2.2 moles) ofthe isobutanol, 152.1 g (1 mole) of 4-cyclohexene-1,2-dicarboxylicanhydride (prepared by usual Diels-Alder reaction of maleic anhydrideand 1,3-butadiene) and toluene (5 wt. % based on the starting materialsfed). Then the mixture was heated to 150° C. in the presence ofp-toluenesulfonic acid catalyst (0.4 wt. % based on the startingmaterials fed) in a nitrogen atmosphere. While water generated duringthe reaction was removed by means of water separator, the esterificationreaction was conducted at 150° C. under reduced pressure (20000 Pa) for6 hours, and the reaction was continued at 150° C. under reducedpressure (10000 Pa) for 2 hours.

After the reaction, the excess isobutanol was removed by distillation at180° C. under a reduced pressure of 1330 Pa, and the obtained liquidresidue was neutralized by adding thereto 22 g of a 4% aqueous solutionof sodium hydroxide and stirring the mixture at 80° C. for 2 hours, andthen washed with water until the aqueous layer became neutral, tothereby give a crude liquid ester. At this point, the crude ester had atotal acid number of 0.01 mgKOH/g. Subsequently, to the ester was addedactivated carbon (“Shirasagi M” manufactured by Sumitomo Chemical Co.,Ltd.; 0.2 wt. % based on the starting materials fed), and the mixturewas stirred at 90° C. and at 1330 Pa for 1 hour and filtered, whereby260 g of diisobutyl 4-cyclohexene-1,2-dicarboxylate was obtained.Dehydration was carried out at 100° C. under a reduced pressure of 1330Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained ester areshown in Table 2. The ester had a hue of 120 in terms of Hazen colornumber, a water content of 20 ppm, a sulfated ash content of less than 1ppm, a sulfur content of 22 ppm, a phosphorus content of less than 1ppm, a hydroxyl value of 0.5 mgKOH/g, a peroxide value of 6.4 meq/kg anda carbonyl value of 15.2.

Comparative Example I-2

Purified diisobutyl 4-cyclohexene-1,2-dicarboxylate was produced in thesame manner as in Comparative Example I-i with the exception of usingisobutanol having a peroxide value of 0.2 meq/kg and a carbonyl value of0.3 (the same as used in Example I-1). Thereafter, dehydration wascarried out at 100° C. under a reduced pressure of 1330 Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained ester areshown in Table 2. The ester had a hue of 20 in terms of Hazen colornumber, a water content of 13 ppm, a sulfated ash content of less than 1ppm, a sulfur content of 25 ppm, a phosphorus content of less than 1ppm, a hydroxyl value of 0.3 mgKOH/g, a peroxide value of 0.2 meq/kg anda carbonyl value of 0.6.

Comparative Example I-3

When 2-ethylhexanol was stored at room temperature for one year, itshowed a peroxide value of 0.7 meq/kg and a carbonyl value of 4.8.Following the procedure of Comparative Example I-1 with the exception ofconducting esterification reaction using the 2-ethylhexanol in thepresence of phosphoric acid catalyst (0.3 wt. % based on the startingmaterials fed) and removing the 2-ethylhexanol by distillation at 210°C. under reduced pressure of 1330 Pa, di(2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate was obtained. Thereafter, dehydrationwas carried out at 130° C. under a reduced pressure of 1330 Pa for 5hours.

The total acid number and kinematic viscosity of the obtained ester areshown in Table 2. The ester had a hue of 100 in terms of Hazen colornumber, a water content of 33 ppm, a sulfated ash content of less than 1ppm, a sulfur content of less than 1 ppm, a phosphorus content of 32ppm, a hydroxyl value of 1.2 mgKOH/g, a peroxide value of 1.3 meq/kg anda carbonyl value of 3.9.

Comparative Example 1-4

When isodecanol was stored at room temperature for one year, it showed aperoxide value of 1.8 meq/kg and a carbonyl value of 3.9. The sameprocedure as in Comparative Example I-1 was carried out except thatesterification reaction was conducted using the isodecanol and tin oxideas a catalyst (0.2 wt. % based on the starting materials fed) at 230° C.for 4 hours and at 230° C. under reduced pressure (20000 Pa) for 1 hour.After the reaction, the procedure of Comparative Example I-1 wasfollowed with the exception of removing excess isodecanol bydistillation at 210° C. under a reduced pressure of 1330 Pa, wherebydiisodecyl 4-cyclohexene-1,2-dicarboxylate was obtained. Thereafter,dehydration was carried out at 130° C. under a reduced pressure of 1330Pa for 5 hours.

The total acid number and kinematic viscosity of the obtained ester areshown in Table 2. The ester had a hue of 70 in terms of Hazen colornumber, a water content of 27 ppm, a sulfated ash content of 2 ppm, asulfur content of less than 1 ppm, a phosphorus content of less than 1ppm, a hydroxyl value of 0.4 mgKOH/g, a peroxide value of 5.0 meq/kg anda carbonyl value of 7.6. TABLE 2 Properties of esters Compa- Kinematicrative Total acid viscosity Exam- number (mm²/s) ple Ester name(mgKOH/g) 40° C. 100° C. I-1 Diisobutyl 4-cyclohexene-1,2- 0.01 9.1 2.1dicarboxylate I-2 Diisobutyl 4-cyclohexene-1,2- 0.01 9.0 2.1dicarboxylate I-3 Di(2-ethylhexyl) 4- 0.01 17.4 3.3 cyclohexene-1,2-dicarboxylate I-4 Diisodecyl 4-cyclohexene-1,2- 0.02 29.0 4.6dicarboxylate

Test Example I-1

Electrical insulating property each of the esters of Examples I-1 toI-10 and Comparative Examples I-1 to I-4 was evaluated in terms ofvolume resistivity. The results are shown in Table 3.

Test Example I-2

Heat stability each of the esters of Examples I-1 to I-10 andComparative Examples I-1 to I-4 was evaluated. The results are shown inTable 3.

Test Example I-3

Long-term hydrolysis stability each of the esters of Examples I-1 toI-10 and Comparative Examples I-1 to I-4 was evaluated. The results areshown in Table 3. TABLE 3 Long-term Heat stability hydrolysis Volume(increased total stability (increased resistivity acid number, totalacid number, Sample (Ω · cm) mgKOH/g) mgKOH/g) Ester of Ex. I-1 8.6 ×10¹¹ 0.53 0.83 Ester of Ex. I-2 9.5 × 10¹¹ 0.48 0.72 Ester of Ex. I-34.5 × 10¹³ 0.44 0.77 Ester of Ex. I-4 1.9 × 10¹³ 0.39 0.82 Ester of Ex.I-5 8.9 × 10¹³ 0.70 0.83 Ester of Ex. I-6 8.5 × 10¹¹ 0.81 0.75 Ester ofEx. I-7 8.1 × 10¹² 0.77 0.68 Ester of Ex. I-8 4.7 × 10¹³ 0.42 0.60 Esterof Ex. I-9 8.2 × 10¹² 0.88 0.97 Ester of Ex. I-10 3.3 × 10¹³ 0.62 0.63Ester of Comp. Ex. I-1 3.2 × 10¹⁰ 3.82 14.82 Ester of Comp. Ex. I-2 3.9× 10¹⁰ 2.99 10.27 Ester of Comp. Ex. I-3 3.1 × 10¹⁰ 3.16 7.56 Ester ofComp. Ex. I-4 4.1 × 10¹² 1.51 3.38

As apparent from Examples I-1 to I-8, the alicyclic dicarboxylic aciddiesters prepared by the process of the present invention are excellentin hue, electrical insulating property, heat stability and hydrolysisstability so that they are suitable for use as a refrigerator oil.

On the other hand, as shown in Comparative Examples I-1 to I-4, theesters prepared by the reaction using a sulfur- or phosphorus-containingcatalyst or the esters prepared using an alcohol having a peroxide valuein excess of 1.0 mgKOH/g are poor in hue and high in peroxide value andcarbonyl value even if neutralization and treatment with an adsorbentare sufficiently carried out. Further, the total acid numbers of theseesters are considerably increased in the test for the evaluation of heatstability and hydrolysis stability, and the volume resistivity thereofis also low in the test for the evaluation of electrical insulatingproperty.

As shown by the results of Examples I-9 and I-10, alicyclic dicarboxylicacid diesters having improved performance can be prepared by purifyingthe produced esters using at least two kinds of adsorbents.

The process of the present invention provides alicyclic dicarboxylicacid diesters which are excellent in electrical insulating property,heat stability and hydrolysis stability and are suited for use as arefrigerator oil.

Embodiment II of the present invention will be described in greaterdetail with reference to the following examples and comparativeexamples. The properties of lubricating oils prepared in these exampleswere evaluated by the following methods.

Kinematic Viscosity

Measured according to JIS-K-2283 using Ubbellohde viscometer.

Total Acid Number

Measured according to JIS-K-2501.

Water Content

Measured according to JIS-K-2275 using Karl Fischer's moisture meter(MKC-510, product of Kyoto Denshi Kabushiki Kaisha)

Sulfated Ash Content

Measured according to JIS-K-2272.5.

Sulfur Content

A sample ester (5.0 g) was diluted with hexane to give a 10.0 mldilution, and the sulfur content of the ester was measured with a sulfuranalyzer, TS-03 (product of Mitsubishi Chemical Corp.).

Phosphorus Content

Measured according to JIS-K-0102-1998.

Hydroxyl Value

Measured according to JIS-K-0070.

Peroxide Value

Measured according to 2.5.2-1996 (Standard Methods for the Analysis ofFats, Oil and Related Materials (Japan Oil Chemists' Society).

Carbonyl Value

Measured according to 2.5.4-1996 (Standard Methods for the Analysis ofFats, Oil and Related Materials (Japan Oil Chemists' Society).

Test for Electrical Insulating Property

The volume resistivity was measured at 25° C. according to JIS-C-2101.The higher the volume resistivity is, the more excellent the electricalinsulating property is.

Test for Hydrolysis Stability

Iron wire, copper wire and aluminum wire, 1.6 mm in diameter and 4 cm inlength, were placed in a glass test tube of 6.6 mm in inner diameter and30 cm in height, and 2.0 g of an ester sample and 0.2 g of distilledwater were weighed out and introduced into the test tube. The test tubewas sealed while it was degassed by an aspirator. The test tube wasplaced in an oven and heated at 175° C. for 30 hours. Then the estersample was taken out to measure the total acid number. It is consideredthat the smaller the increase in total acid number is, the higher thehydrolysis stability is. The result obtained in this test is an index ofhydrolysis resistance of the ester as heated in the presence of water.

Test for Heat Stability

Iron wire, copper wire and aluminum wire, 1.6 mm in diameter and 4 cm inlength were placed in a beaker of 53 mm in inner diameter and 56 mm inheight, and 40 g of an ester sample was weighed out and introduced intothe beaker. The beaker was placed in an oven and heated at 175° C. for15 hours. Then the ester sample was taken out to measure the total acidnumber. The smaller the increase in acid number after the test ascompared with that before the test is, the higher the heat stability is.The result obtained in this test is an index of resistance of the esterto oxidative deterioration.

Analysis by Gas Chromatography

The cis isomer/trans isomer ratio of alicyclic dicarboxylic aciddiesters were determined by gas chromatography, and expressed in termsof area ratio of the obtained gas chromatogram. The proportions of theesters in the ester mixtures were also expressed in terms of area ratioof the obtained gas chromatogram. Measurement conditions and analysisconditions are as follows.

Measurement Conditions:

-   -   Instrument: Gas chromatograph GC-14B (product of Shimadzu        Seisakusho)    -   Column used: 3.2 mm in diameter×3.1 m (made of glass)    -   Column adsorbent: DEGS Chromosorb WAW, liquid phase support        ratio: 15%, 60/80 mesh (GL Science)    -   Injection temperature: 240° C.    -   Column temperature: 180° C.    -   Nitrogen stream: 40 mL/minute    -   Sample concentration: 5 wt. % (dilution solvent:acetone)

Analysis Conditions:

-   -   Data processing apparatus: chromatopack C—R5A (product of        Shimadzu Seishakusho)    -   Analysis parameters: WIDTH=5        -   SLOPE=70        -   DRIFT=0        -   MIN. AREA=1000        -   T.DBL=0

Example II-1

A 4-necked flask equipped with a stirrer, a thermometer and a Dean-Starkwater separator was charged with 152.1 g (1 mole) of4-cyclohexene-1,2-dicarboxylic anhydride (prepared by usual Diels-Alderreaction of maleic anhydride and 1,3-butadiene) and 74 g (1 mole) ofisobutanol as alcohol component 1. The mixture was heated to 130° C. andstirred for 1 hour in a nitrogen atmosphere. At this point, the totalacid number of the reaction mixture was found to be 248 mgKOH/g(theoretical value:248 mgKOH/g).

Then tin hydroxide (0.2 wt. % based on the starting materials fed) wasadded thereto and the mixture was heated to 220° C. At 220° C., 156 g(1.2 moles) of 2-ethylhexanol as alcohol component 2 was added dropwise.While water generated during the reaction was removed by the waterseparator, the esterification reaction was carried out in a nitrogenatmosphere at 220° C. for about 6 hours until the total acid number ofthe reaction mixture became 3 mgKOH/g or less, and further continued at220° C. and at 20000 Pa for 1 hour.

After the reaction, the excess alcohol was removed by distillation at180° C. under a reduced pressure of 1330 Pa, and the obtained liquidresidue was neutralized by adding thereto 27 g of a 4% aqueous solutionof sodium hydroxide and stirring the mixture at 80° C. for 2 hours, andthen washed with water until it became neutral, giving a crude estermixture. At this point, the crude ester mixture had a total acid numberof 0.01 mgKOH/g. Subsequently, to the crude ester mixture was addedactivated carbon (“Shirasagi M” manufactured by Sumitomo Chemical Co.,Ltd.; 0.1 wt. % based on the starting materials fed), and the mixturewas stirred at 90° C. and at 1330 Pa for 1 hour and filtered, whereby311 g of a purified ester mixture containing (isobutyl) (2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate was obtained. Dehydration was carriedout at 100° C. under a reduced pressure of 1330 Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 4. The ester mixture had a water content of23 ppm, a sulfated ash content of less than 1 ppm, a sulfur content ofless than 1 ppm, a phosphorus content of less than 1 ppm, a hydroxylvalue of 0.7 mgKOH/g, a peroxide value of 0.7 meq/kg and a carbonylvalue of 0.2. The obtained ester mixture had a cis:trans isomer ratio of53:47 (area %), as determined from the gas chromatogram thereof.Further, the obtained ester mixture was found to be a mixture of thefollowing esters from the gas chromatogram thereof:

-   -   (1) diisobutyl 4-cyclohexene-1,2-dicarboxylate    -   (2) (isobutyl)(2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate    -   (3) di(2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate        -   (1)/(2)/(3)=14.5/54.7/30.8 (area %)

Example II-2

Following the procedure of Example II-1, 152.1 g (1 mole) of4-cyclohexene-1,2-dicarboxylic anhydride (prepared by usual Diels-Alderreaction of maleic anhydride and 1,3-butadiene), 29.6 g (0.4 mole) ofisobutanol and 78 g (0.6 mole) of 2-ethylhexanol as alcohol component 1were subjected to esterification reaction in a 4-necked flask, wherebythe total acid number of the reaction mixture became 218 mgKOH/g(theoretical value: 219 mgKOH/g).

Then, to the reaction mixture was added tin hydroxide (0.2 wt. % basedon the starting materials fed) as a catalyst, and at 220° C., 156 g (1.2moles) of 2-ethylhexanol as alcohol component 2 was further addeddropwise. While the water generated during the reaction was removed bywater separator, the esterification reaction was carried out at 220° C.for about 6 hours until the total acid number of the reaction mixturebecame 3 mgKOH/g or less, and further continued at 220° C. and at 20000Pa for 1 hour.

After the reaction, the excess alcohol was removed by distillation at180° C. under a reduced pressure of 1330 Pa, and the obtained liquidresidue was neutralized by adding thereto 27 g of a 4% aqueous solutionof sodium hydroxide and stirring the mixture at 80° C. for 2 hours, andthen washed with water until it became neutral, giving a crude estermixture. At this point, the crude ester mixture had a total acid numberof 0.01 mgKOH/g. Subsequently, to the crude ester mixture was addedactivated carbon (“Shirasagi M” manufactured by Sumitomo Chemical Co.,Ltd.; 0.1 wt. % based on the starting materials fed), and the mixturewas stirred at 90° C. and at 1330 Pa for 1 hour and filtered, whereby346 g of a purified ester mixture containing (isobutyl) (2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate was obtained. Dehydration was carriedout at 100° C. under a reduced pressure of 1330 Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 4. The ester mixture had a water content of15 ppm, a sulfated ash content of 3 ppm, a sulfur content of less than 1ppm, a phosphorus content of less than 1 ppm, a hydroxyl value of 0.4mgKOH/g, a peroxide value of 0.2 meq/kg and a carbonyl value of 0.5. Theobtained ester mixture had a cis:trans isomer ratio of 55:45 (area %),as determined from the gas chromatogram thereof. Further, the obtainedester mixture was found to be a mixture of the following esters from thegas chromatogram thereof:

-   -   (1) diisobutyl 4-cyclohexene-1,2-dicarboxylate    -   (2) (isobutyl)(2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate    -   (3) di(2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate        -   (1)/(2)/(3)=2.0/23.5/74.5 (area %).

Example II-3

Following the procedure of Example II-1, 152.1 g (1 mole) of4-cyclohexene-1,2-dicarboxylic anhydride (prepared by usual Diels-Alderreaction of maleic anhydride and 1,3-butadiene) and 74 g (1.0 mole) ofisobutanol as alcohol component 1 were subjected to a reaction in afour-necked flask, whereby the total acid number of the reaction mixturebecame 249 mgKOH/g (theoretical value: 248 mgKOH/g).

Then, to the reaction mixture was added tin hydroxide (0.2 wt. % basedon the starting materials fed) as a catalyst, and at 220° C., 64.4 g(0.87 mole) of isobutanol and 42.9 g (0.33 mole) of 2-ethylhexanol asalcohol component 2 were further added dropwise. While water generatedduring the reaction was removed by water separator, the esterificationreaction was carried out at 220° C. for about 6 hours until the totalacid number of the reaction mixture became 3 mgKOH/g or less, andfurther continued at 220° C. and at 20000 Pa for 1 hour.

After the reaction, the excess alcohols were removed by distillation at180° C. under a reduced pressure of 1330 Pa, and the obtained liquidresidue was neutralized by adding thereto 27 g of a 4% aqueous solutionof sodium hydroxide and stirring the mixture at 80° C. for 2 hours, andthen washed with water until it became neutral, giving a crude estermixture. At this point, the crude ester mixture had a total acid numberof 0.01 mgKOH/g. Subsequently, to the crude ester mixture was addedactivated carbon (“Shirasagi M” manufactured by Sumitomo Chemical Co.,Ltd.; 0.1 wt. % based on the starting materials fed), and the mixturewas stirred at 90° C. and at 1330 Pa for 1 hour and filtered, whereby282 g of a purified ester mixture containing (isobutyl) (2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate was obtained. Dehydration was carriedout at 100° C. under a reduced pressure of 1330 Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 4. The ester mixture had a water content of12 ppm, a sulfated ash content of 2 ppm, a sulfur content of less than 1ppm, a phosphorus content of less than 1 ppm, a hydroxyl value of 1.1mgKOH/g, a peroxide value of 0.6 meq/kg and a carbonyl value of 0.9. Theobtained ester mixture had a cis:trans isomer ratio of 42:58 (area %),as determined from the gas chromatogram thereof. Further, the obtainedester mixture was found to be a mixture of the following esters from thegas chromatogram thereof:

-   -   (1) diisobutyl 4-cyclohexene-1,2-dicarboxylate    -   (2) (isobutyl)(2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate    -   (3) di(2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate        -   (1)/(2)/(3)=71.6/25.7/2.7 (area %)

Example II-4

A reaction was carried out following the procedure of Example II-1 andusing 152.1 g (1 mole) of 4-cyclohexene-1,2-dicarboxylic anhydride(prepared by usual Diels-Alder reaction of maleic anhydride and1,3-butadiene), 51.8 g (0.7 mole) of isobutanol and 43.2 g (0.3 mole) ofisononanol (“Oxocol 900”, product of Kyowa Hakko Kogyo. Co., Ltd.) asalcohol component 1, whereby the total acid number of the reactionmixture became 233 mgKOH/g (theoretical value: 231 mgKOH/g).

Then, to the reaction mixture was added tetraisopropyl titanate (0.3 wt.% based on the starting materials fed), and at 210° C., 172.8 g (1.2moles) of isononanol as alcohol component 2 was further added dropwise.While water generated during the reaction was removed by waterseparator, the esterification reaction was carried out at 210° C. forabout 6 hours until the total acid number of the reaction mixture became3 mgKOH/g or less, and further continued at 210° C. and at 20000 Pa for1 hour.

After the reaction, the excess alcohols were removed by distillation at180° C. under a reduced pressure of 1330 Pa, and the obtained liquidresidue was neutralized by adding thereto 27 g of a 4% aqueous solutionof sodium hydroxide and stirring the mixture at 80° C. for 2 hours, andthen washed with water until it became neutral, giving a crude estermixture. At this point, the crude ester mixture had a total acid numberof 0.01 mgKOH/g. Subsequently, to the crude ester mixture was addedactivated carbon (“Shirasagi M” manufactured by Sumitomo Chemical Co.,Ltd.; 0.1 wt. % based on the starting materials fed), and the mixturewas stirred at 90° C. and at 1330 Pa for 1 hour and filtered, whereby346 g of a purified ester mixture containing (isobutyl) (isononyl)4-cyclohexene-1,2-dicarboxylate was obtained. Dehydration was carriedout at 100° C. under a reduced pressure of 1330 Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 4. The ester mixture had a water content of10 ppm, a sulfated ash content of less than 1 ppm, a sulfur content ofless than 1 ppm, a phosphorus content of less than 1 ppm, a hydroxylvalue of 0.7 mgKOH/g, a peroxide value of 0.7 meq/kg and a carbonylvalue of 0.5. The obtained ester mixture had a cis:trans isomer ratio of80:20 (area %), as determined from the gas chromatogram thereof.Further, the obtained ester mixture was found to be a mixture of thefollowing esters from the gas chromatogram thereof:

-   (1) diisobutyl 4-cyclohexene-1,2-dicarboxylate-   (2) (isobutyl)(isononyl) 4-cyclohexene-1,2-dicarboxylate-   (3) diisononyl 4-cyclohexene-1,2-dicarboxylate    (1)/(2)/(3)=6.6/43.2/50.2 (area %)

Example II-5

A reaction was carried out following the procedure of Example II-1 andusing 152.1 g (1 mole) of 4-cyclohexene-1,2-dicarboxylic anhydride(prepared by usual Diels-Alder reaction of maleic anhydride and1,3-butadiene) and 74 g (1 mole) of isobutanol as alcohol component 1,whereby the total acid number of the reaction mixture became 247 mgKOH/g(theoretical value: 248 mgKOH/g).

Then, to the reaction mixture was added tin hydroxide (0.2 wt. % basedon the starting materials fed) as a catalyst, and at 220° C., 7.4 g (0.1mole) of isobutanol and 158.4 g (1.1 moles) of 3,5,5-trimethylhexanol asalcohol component 2 were further added dropwise. While water generatedduring the reaction was removed by water separator, the esterificationreaction was carried out at 220° C. for about 6 hours until the totalacid number of the reaction mixture became 3 mgKOH/g or less, andfurther continued at 220° C. and at 20000 Pa for 1 hour.

After the reaction, the excess alcohols were removed by distillation at180° C. under a reduced pressure of 1330 Pa, and the obtained liquidresidue was neutralized by adding thereto 35 g of a 4% aqueous solutionof sodium hydroxide and stirring the mixture at 80° C. for 2 hours, andthen washed with water until it became neutral, giving a crude estermixture. At this point, the crude ester mixture had a total acid numberof 0.01 mgKOH/g. Subsequently, to the crude ester mixture was addedactivated carbon (“Shirasagi M” manufactured by Sumitomo Chemical Co.,Ltd.; 0.1 wt. % based on the starting materials fed), and the mixturewas stirred at 90° C. and at 1330 Pa for 1 hour and filtered, whereby334 g of a purified ester mixture containing (isobutyl)(3,5,5-trimethylhexyl) 4-cyclohexene-1,2-dicarboxylate was obtained.Dehydration was carried out at 100° C. under a reduced pressure of 1330Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 4. The ester mixture had a water content of28 ppm, a sulfated ash content of 1 ppm, a sulfur content of less than 1ppm, a phosphorus content of less than 1 ppm, a hydroxyl value of 0.7mgKOH/g, a peroxide value of 0.9 meq/kg and a carbonyl value of 1.1. Theobtained ester had a cis:trans isomer ratio of 51:49 (area %), asdetermined from the gas chromatogram thereof. Further, the obtainedester mixture was found to be a mixture of the following esters from thegas chromatogram thereof:

-   -   (1) diisobutyl 4-cyclohexene-1,2-dicarboxylate    -   (2) (isobutyl) (3,5,5-trimethylhexyl)        4-cyclohexene-1,2-dicarboxylate    -   (3) di(3,5,5-trimethylhexyl) 4-cyclohexene-1,2-dicarboxylate        -   (1)/(2)/(3)=17.9/56.1/26.0 (area %

Example II-6

A reaction was carried out following the procedure of Example II-1 andusing 154.1 g (1 mole) of 1,2-cyclohexanedicarboxylic anhydride(prepared by hydrogenating 4-cyclohexene-1,2-dicarboxylic anhydrideobtained by usual Diels-Alder reaction of maleic anhydride and1,3-butadiene) and 74 g of isobutanol (1 mole) as alcohol component 1,whereby the total acid number of the reaction mixture became 247 mgKOH/g(theoretical value: 246 mgKOH/g).

Then, to the reaction mixture was added tin hydroxide (0.2 wt. % basedon the starting materials fed) as a catalyst, and at 220° C., 156 g (1.2moles) of 2-ethylhexanol as alcohol component 2 was further addeddropwise. While water generated during the reaction was removed by waterseparator, the esterification reaction was carried out at 220° C. forabout 6 hours until the total acid number of the reaction mixture became3 mgKOH/g or less, and further continued at 220° C. and at 20000 Pa for1 hour.

After the reaction, the excess alcohols were removed by distillation at180° C. under a reduced pressure of 1330 Pa, and the obtained liquidresidue was neutralized by adding thereto 27 g of a 4% aqueous solutionof sodium hydroxide and stirring the mixture at 80° C. for 2 hours, andthen washed with water until it became neutral, giving a crude estermixture. At this point, the crude ester mixture had a total acid numberof 0.01 mgKOH/g. Subsequently, to the crude ester mixture was addedactivated carbon (“Shirasagi M” manufactured by Sumitomo Chemical Co.,Ltd.; 0.1 wt. % based on the starting materials fed), and the mixturewas stirred at 90° C. and at 1330 Pa for 1 hour and filtered, whereby311 g of a purified ester mixture containing (isobutyl) (2-ethylhexyl)1,2-cyclohexanedicarboxylate was obtained. Dehydration was carried outat 100° C. under a reduced pressure of 1330 Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 4. The ester mixture had a water content of12 ppm, a sulfated ash content of less than 1 ppm, a sulfur content ofless than 1 ppm, a phosphorus content of less than 1 ppm, a hydroxylvalue of 1.3 mgKOH/g, a peroxide value of 0.5 meq/kg and a carbonylvalue of 0.6. The obtained ester had a cis trans isomer ratio of 39:61(area %), as determined from the gas chromatogram thereof. Further theobtained ester mixture was found to be a mixture of the following estersfrom the gas chromatogram thereof:

-   (1) diisobutyl 1,2-cyclohexanedicarboxylate-   (2) (isobutyl)(2-ethylhexyl) 1,2-cyclohexanedicarboxylate-   (3) di(2-ethylhexyl) 1,2-cyclohexanedicarboxylate

(1)/(2)/(3)=13.9/52.9/33.2 (area %) TABLE 4 Properties of estersKinematic Total acid viscosity number (mm²/s) Example Acid componentAlcohol component (mgKOH/g) 40° C. 100° C. II-1 4-Cyclohexene-1,2-Isobutanol (45 mole %) 0.01 13.1 2.7 dicarboxylic acid 2-Ethylhexanol(55 mole %) II-2 4-Cyclohexene-1,2- Isobutanol (18 mole %) 0.01 15.2 3.1dicarboxylic acid 2-Ethylhexanol (82 mole %) II-3 4-Cyclohexene-1,2-Isobutanol (85 mole %) 0.01 9.2 2.2 dicarboxylic acid 2-Ethylhexanol (15mole %) II-4 4-Cyclohexene-1,2- Isobutanol (32 mole %) 0.01 16.5 3.3dicarboxylic acid Isononanol (68 mole %) II-5 4-Cyclohexene-1,2-Isobutanol (50 mole %) 0.01 15.3 3.0 dicarboxylic acid 3,5,5-Trimethylhexanol (50 mole %) II-6 1,2-Cyclohexane- Isobutanol (45 mole%) 0.01 13.0 2.7 dicarboxylic acid 2-Ethylhexanol (55 mole %)

Comparative Example II-1

A reaction was carried out following the procedure of Example II-1 using152.1 g (1 mole) of 4-cyclohexene-1,2-dicarboxylic anhydride (preparedby usual Diels-Alder reaction of maleic anhydride and 1,3-butadiene) and74 g (1 mole) of isobutanol as alcohol component 1, whereby the totalacid number of the reaction mixture became 248 mgKOH/g (theoreticalvalue: 248 mgKOH/g).

Then, to the reaction mixture was added p-toluenesulfonic acid (0.4 wt.% based on the starting materials fed) as a catalyst, and at 220° C.,156 g (1.2 moles) of 2-ethylhexanol as alcohol component 2 was furtheradded dropwise. While water generated during the reaction was removed bywater separator, the esterification reaction was carried out at 220° C.for about 6 hours until the total acid number of the reaction mixturebecame 3 mgKOH/g or less, and further continued at 220° C. and at 20000Pa for 1 hour.

After the reaction, the excess alcohols were removed by distillation at180° C. under a reduced pressure of 1330 Pa, and the obtained liquidresidue was neutralized by adding thereto 27 g of a 4% aqueous solutionof sodium hydroxide and stirring the mixture at 80° C. for 2 hours, andthen washed with water until it became neutral, giving a crude estermixture. At this point, the crude ester mixture had a total acid numberof 0.01 mgKOH/g. Subsequently, to the crude ester mixture was addedactivated carbon (“Shirasagi M” manufactured by Sumitomo Chemical Co.,Ltd.; 0.1 wt. % based on the starting materials fed), and the mixturewas stirred at 90° C. and at 1330 Pa for 1 hour and filtered, whereby313 g of a purified ester mixture containing (isobutyl) (2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate was obtained. Dehydration was carriedout at 100° C. under a reduced pressure of 1330 Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 5. The ester mixture had a water content of12 ppm, a sulfated ash content of less than 1 ppm, a sulfur content of28 ppm, a phosphorus content of less than 1 ppm, a hydroxyl value of 0.4mgKOH/g, a peroxide value of 0.1 meq/kg and a carbonyl value of 0.3. Theobtained ester mixture had a cis:trans isomer ratio of 46:54 (area %),as determined from the gas chromatogram thereof. Further the obtainedester mixture was found to be a mixture of the following esters from thegas chromatogram thereof:

-   (1) diisobutyl 4-cyclohexene-1,2-dicarboxylate-   (2) (isobutyl)(2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate-   (3) di(2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate    -   (1)/(2)/(3)=14.2/53.9/31.9 (area %)

Comparative Example II-2

A reaction was carried out in the same apparatus as used in ComparativeExample II-1 and using 152.1 g (1 mole) of4-cyclohexene-1,2-dicarboxylic anhydride (prepared by usual Diels-Alderreaction of maleic anhydride and 1,3-butadiene), 74 g (1 mole) ofisobutanol and 156 g (1.2 moles) of 2-ethylhexanol. Then the mixture wasgradually heated to 210° C. in the presence of tetraisopropyl titanate(0.2 wt. % based on the starting materials fed) to undergoesterification reaction for 26 hours. More specifically, while watergenerated during the reaction was removed by means of the waterseparator, the esterification reaction was conducted at 210° C. forabout 22 hours until the total acid number of the reaction mixturebecame 3 mgKOH/g or less. Thereafter, the reaction was continued at 210°C. and at 20000 Pa for about 4 hours. The reaction mixture was worked up(evaporation of excess alcohols, neutralization, washing with water andtreatment with adsorbent) in the same manner as in comparative ExampleII-1 to give 302 g of purified ester mixture containing (isobutyl)(2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate. Dehydration was carriedout at 100° C. under a reduced pressure of 1330 Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 5. The ester mixture had a water content of22 ppm, a sulfated ash content of 2 ppm, a sulfur content of less than 1ppm, a phosphorus content of less than 1 ppm, a hydroxyl value of 0.8mgKOH/g, a peroxide value of 3.1 meq/kg and a carbonyl value of 2.6. Theobtained ester mixture had a cis:trans isomer ratio of 78:22 (area %),as determined from the gas chromatogram thereof. Further, the obtainedester mixture was found to be a mixture of the following esters from thegas chromatogram thereof:

-   (1) diisobutyl 4-cyclohexene-1,2-dicarboxylate-   (2) (isobutyl) (2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate-   (3) di(2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate

(1)/(2)/(3)=13.6/54.1/32.3 (area %) TABLE 5 Properties of estersKinematic Total acid viscosity Comp. number (mm²/s) Ex.   Acid componentAlcohol component (mgKOH/g) 40° C. 100° C. II-1 4-Cyclohexene-1,2-Isobutanol (45 mole %) 0.01 13.3 2.7 dicarboxylic acid 2-Ethylhexanol(55 mole %) II-2 4-Cyclohexene-1,2- Isobutanol (45 mole %) 0.01 13.4 2.7dicarboxylic acid 2-Ethylhexanol (55 mole %)

Example II-7

A 4-necked flask equipped with a stirrer, a thermometer and a Dean-Starkwater separator was charged with 152.1 g (1 mole) of4-cyclohexene-1,2-dicarboxylic anhydride (prepared by usual Diels-Alderreaction of maleic anhydride and 1,3-butadiene) and 29.6 g (0.4 mole) ofisobutanol having a peroxide value of 0.1 meq/kg and a carbonyl value of0.1 and 78 g (0.6 mole) of 2-ethylhexanol having a peroxide value of 0.2meq/kg and a carbonyl value of 0.1 as alcohol component 1. The mixturewas heated to 130° C. and stirred for 1 hour in a nitrogen atmosphere.At this point, the total acid number of the reaction mixture was foundto be 248 mgKOH/g (theoretical value:248 mgKOH/g).

Then tin hydroxide (0.2 wt. % based on the starting materials fed) wasadded thereto and the mixture was heated to 220° C. At 220° C., 156 g(1.2 moles) of 2-ethylhexanol having a peroxide value of 0.2 meq/kg anda carbonyl value of 0.1 as alcohol component 2 was further addeddropwise. While water generated during the reaction was removed by thewater separator, the esterification reaction was carried out at 220° C.for about 6 hours in a nitrogen atmosphere, and further continued at220° C. and at 20000 Pa for 1 hour.

After the reaction, the excess alcohols were removed by distillation at180° C. under a reduced pressure of 1330 Pa, and the obtained liquidresidue was neutralized by adding thereto 27 g of a 4% aqueous solutionof sodium hydroxide and stirring the mixture at 80° C. for 2 hours, andthen washed with water until it became neutral, giving a crude estermixture. At this point, the crude ester mixture had a total acid numberof 0.01 mgKOH/g. Subsequently, to the crude ester mixture was addedactivated carbon (“Shirasagi M” manufactured by Sumitomo Chemical Co.,Ltd.; 0.1 wt. % based on the starting materials fed), and the mixturewas stirred at 90° C. and at 1330 Pa for 1 hour and filtered, whereby314 g of a purified ester mixture containing (isobutyl)(2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate was obtained. Dehydrationwas carried out at 100° C. under a reduced pressure of 1330 Pa for 6hours. The total acid number and kinematic viscosity of the obtainedester mixture are shown in Table 6. The ester mixture had a watercontent of 14 ppm, a sulfated ash content of less than 1 ppm, a sulfurcontent of less than 1 ppm, a phosphorus content of less than 1 ppm, ahydroxyl value of 0.3 mgKOH/g, a peroxide value of 0.2 meq/kg and acarbonyl value of 0.2. The obtained ester mixture had a cis:trans isomerratio of 48:52 (area %), as determined from the gas chromatogramthereof. Further the obtained ester mixture was found to be a mixture ofthe following esters from the gas chromatogram thereof:

-   (1) diisobutyl 4-cyclohexene-1,2-dicarboxylate-   (2) (isobutyl)(2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate-   (3) di(2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate    -   (1)/(2)/(3)=15.0/52.6/32.4 (area %)

Example II-8

The same procedure as in Example II-2 was conducted with the exceptionof using isobutanol with a peroxide value of 0.1 meq/kg and a carbonylvalue of 0.1 and 2-ethylhexanol with a peroxide value of 0.2 meq/kg anda carbonyl value of 0.1 as alcohol component 1 and using 2-ethylhexanolwith a peroxide value of 0.2 meg/kg and a carbonyl value of 0.1 asalcohol component 2 and tin oxide (0.2 wt. % based on the startingmaterials fed) as a catalyst, and using, after the neutralization andwashing with water, activated carbon (“Shirasagi M” manufactured bySumitomo Chemical Co., Ltd.; 0.1 wt. % based on the starting materialsfed), activated clay (“Galleon earth V₁” manufactured by MizusawaIndustrial Chemicals Ltd.; 0.1 wt. % based on the starting materialsfed) and synthetic hydrotalcite (“Kyoward 600” manufactured by KyowaKagaku Kogyo Kabushiki Kaisha; 0.2 wt. % based on the starting materialsfed), whereby a purified ester mixture containing (isobutyl)(2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate was produced. Dehydrationwas carried out at 100° C. under a reduced pressure of 1330 Pa for 6hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 6. The ester mixture had a water content of12 ppm, a sulfated ash content of less than 1 ppm, a sulfur content ofless than 1 ppm, a phosphorus content of less than 1 ppm, a hydroxylvalue of 0.5 mgKOH/g, a peroxide value of 0.1 meq/kg and a carbonylvalue of 0.4. The obtained ester mixture had a cis:trans isomer ratio of56:44 (area %), as determined from the gas chromatogram thereof. Furtherthe obtained ester mixture was found to be a mixture of the followingesters from the gas chromatogram thereof:

-   (1) diisobutyl 4-cyclohexene-1,2-dicarboxylate-   (2) (isobutyl)(2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate-   (3) di(2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate    -   (1)/(2)/(3)=1.9/25.1/73.0 (area %)

Example II-9

The same procedure as in Example II-3 was conducted with the exceptionof using isobutanol with a peroxide value of 0.1 meq/kg and a carbonylvalue of 0.1 as alcohol component 1 and isobutanol with a peroxide valueof 0.1 meq/kg and a carboxyl value of 0.1 and 2-ethylhexanol with aperoxide value of 0.2 meq/kg and a carbonyl value of 0.1 as alcoholcomponent 2 and tin oxide (0.2 wt. % based on the starting materialsfed) as a catalyst, whereby a purified ester mixture containing(isobutyl) (2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate was produced.Dehydration was carried out at 100° C. under a reduced pressure of 1330Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 6. The ester mixture had a water content of22 ppm, a sulfated ash content of less than 1 ppm, a sulfur content ofless than 1 ppm, a phosphorus content of less than 1 ppm, a hydroxylvalue of 1.0 mgKOH/g, a peroxide value of 0.1 meq/kg and a carbonylvalue of 0.2. The obtained ester mixture had a cis:trans isomer ratio of50:50 (area %), as determined from the gas chromatogram thereof.Further, the obtained ester mixture was found to be a mixture of thefollowing esters from the gas chromatogram thereof:

-   (1) diisobutyl 4-cyclohexene-1,2-dicarboxylate-   (2) (isobutyl)(2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate-   (3) di(2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate    -   (1)/(2)/(3)=71.9/24.7/3.4 (area %)

Example II-10

Following the procedure of Example II-1, 152.1 g (1 mole) of4-cyclohexene-1,2-dicarboxylic anhydride (prepared by usual Diels-Alderreaction of maleic anhydride and 1,3-butadiene) was reacted with 74 g(1.0 mole) of isobutanol with a peroxide value of 0.1 meq/kg and acarbonyl value of 0.1 as alcohol component 1 in a four-necked flask,whereby the total acid number of the reaction mixture became 248 mgKOH/g(theoretical value: 248 mgKOH/g).

Then, to the reaction mixture was added tin oxide (0.2 wt. % based onthe starting materials fed), and at 220° C. 7.4 g (0.1 mole) of saidisobutanol and 143 g (1.1 moles) of 2-ethylhexanol with a peroxide valueof 0.2 meq/kg and a carbonyl value of 0.1 as alcohol component 2 werefurther added dropwise. While water generated during the reaction wasremoved by water separator, the esterification reaction was carried outat 200° C. for about 6 hours until the total acid number of the reactionmixture became 3 mgKOH/g or less, and further continued at 220° C. andat 20000 Pa for 1 hour.

After the reaction, the excess alcohols were removed by distillation at180° C. under a reduced pressure of 1330 Pa, and the obtained liquidresidue was neutralized by adding thereto 27 g of a 4% aqueous solutionof sodium hydroxide and stirring the mixture at 80° C. for 2 hours, andthen washed with water until it became neutral, giving a crude estermixture. At this point, the crude ester mixture had a total acid numberof 0.01 mgKOH/g. Subsequently, to the crude ester mixture was addedactivated carbon (“Shirasagi M” manufactured by Sumitomo Chemical Co.,Ltd.; 0.1 wt. % based on the starting materials fed), and the mixturewas stirred at 90° C. and at 1330 Pa for 1 hour and filtered, whereby305 g of a purified ester mixture containing (isobutyl) (2-ethylhexyl)4-cyclohexene-1,2-dicarboxylate was obtained. Dehydration was carriedout at 100° C. under a reduced pressure of 1330 Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 6. The ester mixture had a water content of16 ppm, a sulfated ash content of less than 1 ppm, a sulfur content ofless than 1 ppm, a phosphorus content of less than 1 ppm, a hydroxylvalue of 0.3 mgKOH/g, a peroxide value of 0.5 meq/kg and a carbonylvalue of 0.6. The obtained ester mixture had a cis:trans isomer ratio of48:52 (area %), as determined from the gas chromatogram thereof.Further, the obtained ester mixture was found to be a mixture of thefollowing esters from the gas chromatogram thereof:

-   (1) diisobutyl 4-cyclohexene-1,2-dicarboxylate-   (2) (isobutyl)(2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate-   (3) di(2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate    -   (1)/(2)/(3)=19.7/43.8/36.5 (area %)

Example II-11

The same procedure as in Example II-4 was conducted with the exceptionof using isobutanol with a peroxide value of 0.1 meq/kg and a carbonylvalue of 0.1 and isononanol with a peroxide value of 0.2 meq/kg and acarbonyl value of 0.3 as alcohol component 1 and using isononanol with aperoxide value of 0.2 meq/kg and a carbonyl value of 0.3 as alcoholcomponent 2 and using tin oxide (0.2 wt. % based on the startingmaterials fed) as a catalyst, whereby a purified ester mixturecontaining (isobutyl) (isononyl) 4-cyclohexene-1,2-dicarboxylate wasobtained. Dehydration was carried out at 100° C. under a reducedpressure of 1330 Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 6. The ester mixture had a water content of20 ppm, a sulfated ash content of less than 1 ppm, a sulfur content ofless than 1 ppm, a phosphorus content of less than 1 ppm, a hydroxylvalue of 0.7 mgKOH/g, a peroxide value of 0.4 meq/kg and a carbonylvalue of 0.1. The obtained ester mixture had a cis:trans isomer ratio of78:22 (area %), as determined from the gas chromatogram thereof.Further, the obtained ester mixture was found to be a mixture of thefollowing esters from the gas chromatogram thereof:

-   (1) diisobutyl 4-cyclohexene-1,2-dicarboxylate-   (2) (isobutyl)(isononyl) 4-cyclohexene-1,2-dicarboxylate-   (3) di(isononyl) 4-cyclohexene-1,2-dicarboxylate    -   (1)/(2)/(3)=6.6/42.9/50.5 (area %)

Example II-12

The same procedure as in Example II-5 was conducted with the exceptionof using isobutanol with a peroxide value of 0.1 meq/kg and a carbonylvalue of 0.1 as alcohol component 1, isobutanol with a peroxide value of0.1 meq/kg and a carbonyl value of 0.1 and 3,5,5-trimethylhexanol with aperoxide value of 0.1 meq/kg and a carbonyl value of 0.2 as alcoholcomponent 2, and tin oxide (0.2 wt. % based on the starting materialsfed) as a catalyst, whereby a purified ester mixture containing(isobutyl) (3,5,5-trimethylhexyl) 4-cyclohexene-1,2-dicarboxylate wasproduced. Dehydration was carried out at 100° C. under a reducedpressure of 1330 Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 6. The ester mixture had a water content of13 ppm, a sulfated ash content of less than 1 ppm, a sulfur content ofless than 1 ppm, a phosphorus content of less than 1 ppm, a hydroxylvalue of 0.4 mgKOH/g, a peroxide value of 0.2 meq/kg and a carbonylvalue of 0.2. The obtained ester mixture had a cis:trans isomer ratio of57:43 (area %), as determined from the gas chromatogram thereof. Furtherthe obtained ester mixture was found to be a mixture of the followingesters from the gas chromatogram thereof:

-   (1) diisobutyl 4-cyclohexene-1,2-dicarboxylate-   (2) (isobutyl)(3,5,5-trimethylhexyl) 4-cyclohexene-1,2-dicarboxylate-   (3) di(3,5,5-trimethylhexyl) 4-cyclohexene-1,2-dicarboxylate    -   (1)/(2)/(3)=18.0/52.2/29.8 (area %)

Example II-13

Following the procedure of Example II-12, a reaction as carried outusing 152.1 g (1 mole) of 4-cyclohexene-1,2-dicarboxylic anhydride(prepared by usual Diels-Alder reaction of maleic anhydride and1,3-butadiene), 32.6 g (0.44 mole) of isobutanol with a peroxide valueof 0.1 meq/kg and a carbonyl value of 0.1 and 80.6 g (0.56 mole) of3,5,5-trimethylhexanol with a peroxide value of 0.1 meq/kg and acarbonyl value of 0.2 as alcohol component 1, whereby the total acidnumber of the reaction mixture became 217 mgKOH/g (theoretical value:214 mgKOH/g).

Then, to the reaction mixture was added tin oxide (0.2 wt. % based onthe starting materials fed), and at 220° C., 172.8 g (1.1 moles) of3,5,5-trimethylhexanol with a peroxide value of 0.1 meq/kg and acarbonyl value of 0.2 as alcohol component 2 was further added dropwise.While water generated during the reaction was removed by waterseparator, the esterification reaction was carried out at 220° C. forabout 6 hours until the total acid number of the reaction mixture became3 mgKOH/g or less, and further continued at 220° C. and at 20000 Pa for1 hour.

After the reaction, the excess alcohols were removed by distillation at180° C. under a reduced pressure of 1330 Pa, and the obtained liquidresidue was neutralized by adding thereto 33 g of a 4% aqueous solutionof sodium hydroxide and stirring the mixture at. 80° C. for 2 hours, andthen washed with water until it became neutral, giving a crude estermixture. At this point, the crude ester mixture 0.5 had a total acidnumber of 0.01 mgKOH/g. Subsequently, to the crude ester mixture wasadded activated carbon (“Shirasagi M” manufactured by Sumitomo ChemicalCo., Ltd.; 0.1 wt. % based on the starting materials fed), and themixture was stirred at 90° C. and at 1330 Pa for 1 hour and filtered,whereby 383 g of a purified ester mixture containing (isobutyl)(3,5,5-trimethylhexanol) 4-cyclohexene-1,2-dicarboxylate was obtained.Dehydration was carried out at 100° C. under a reduced pressure of 1330Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 6. The ester mixture had a water content of19 ppm, a sulfated ash content of less than 1 ppm, a sulfur content ofless than 1 ppm, a phosphorus content of less than 1 ppm, a hydroxylvalue of 0.7 mgKOH/g, a peroxide value of 0.2 meq/kg and a carbonylvalue of 0.2., The obtained ester mixture had a cis:trans isomer ratioof 56:44 (area %), as determined from the gas chromatogram thereof.Further, the obtained ester mixture was found to be a mixture of thefollowing esters from the gas chromatogram thereof:

-   (1) diisobutyl 4-cyclohexene-1,2-dicarboxylate-   (2) (isobutyl)(3,5,5-trimethylhexyl) 4-cyclohexene-1,2-dicarboxylate-   (3) di(3,5,5-trimethylhexyl)₄-cyclohexene-1,2-dicarboxylate    -   (1)/(2)/(3)=2.3/28.0/69.7 (area %)

Example II-14

The same procedure as in Example II-6 was conducted with the exceptionof using isobutanol with a peroxide value of 0.1 meq/kg and a carbonylvalue of 0.1 as alcohol component 1,2-ethylhexanol with a peroxide valueof 0.2 meq/kg and a carbonyl value of 0.1 as alcohol component 2, givinga purified ester mixture containing (isobutyl)(2-ethylhexyl)1,2-cyclohexanedicarboxylate. Dehydration was carried out at 100° C.under a reduced pressure of 1330 Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 6. The ester mixture had a water content of17 ppm, a sulfated ash content of less than 1 ppm, a sulfur content ofless than 1 ppm, a phosphorus content of less than 1 ppm, a hydroxylvalue of 0.8 mgKOH/g, a peroxide value of 0.1 meq/kg and a carbonylvalue of 0.3. The obtained ester mixture had a cis:trans isomer ratio of38:62 (area %), as determined from the gas chromatogram thereof.Further, the obtained ester mixture was found to be a mixture of thefollowing esters from the gas chromatogram thereof:

-   (1) diisobutyl 1,2-cyclohexanedicarboxylate-   (2) (isobutyl)(2-ethylhexyl) 1,2-cyclohexanedicarboxylate-   (3) di(2-ethylhexyl) 1,2-cyclohexanedicarboxylate    -   (1)/(2)/(3)=14.1/52.6/33.3 (area %)

Example II-15

In the same manner as in Example II-6, a reaction was conducted using154.1 g (1 mole) of 1,2-cyclohexanedicarboxylic anhydride (prepared byhydrogenating 4-cyclohexene-1,2-dicarboxylic anhydride obtained by usualDiels-Alder reaction of maleic anhydride and 1,3-butadiene) and 74 g (1mole) of isobutanol with a peroxide value of 0.1 meq/kg and a carbonylvalue of 0.1 as alcohol component 1, whereby the total acid number ofthe reaction mixture became 248 mgKOH/g (theoretical value: 246mgKOH/g).

Then, to the reaction mixture was added tin oxide (0.2 wt. % based onthe starting materials fed), and at 220° C., 7.4 g (0.1 mole) ofisobutanol with a peroxide value of 0.1 meq/kg and a carbonyl value of0.1 and 143 g (1.1 moles) of 2-ethylhexanol with a peroxide value of 0.2meq/kg and a carbonyl value of 0.1 as alcohol component 2 was furtheradded dropwise. While water generated during the reaction was removed bywater separator, the esterification reaction was carried out at 220° C.for about 9 hours until the total acid number of the reaction mixturebecame 3 mgKOH/g or less, and further continued at 220° C. and at 20000Pa for 1 hour.

After the reaction, the excess alcohols were removed by distillation at180° C. under a reduced pressure of 1330 Pa, and the obtained liquidresidue was neutralized by adding thereto 27 g of a 4% aqueous solutionof sodium hydroxide and stirring the mixture at 80° C. for 2 hours, andthen washed with water until it became neutral, giving a crude estermixture. At this point, the crude ester mixture had a total acid numberof 0.01 mgKOH/g. Subsequently, to the crude ester mixture was addedactivated carbon (“Shirasagi M” manufactured by Sumitomo Chemical Co.,Ltd.; 0.1 wt. % based on the starting materials fed), and the mixturewas stirred at 90° C. and at 1330 Pa for 1 hour and filtered, whereby308 g of a purified ester mixture containing (isobutyl) (2-ethylhexyl)1,2-cyclohexanedicarboxylate was obtained. Dehydration was carried outat 100° C. under a reduced pressure of 1330 Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 6. The ester mixture had a water content of26 ppm, a sulfated ash content of less than 1 ppm, a sulfur content ofless than 1 ppm, a phosphorus content of less than 1 ppm, a hydroxylvalue of 0.9 mgKOH/g, a peroxide value of 0.4 meq/kg and a carbonylvalue of 0.4.

The obtained ester mixture had a dis:trans isomer ratio of 30:70 (area%), as determined from the gas chromatogram thereof. Further, theobtained ester mixture was found to be a mixture of the following estersfrom the gas chromatogram thereof:

-   (1) diisobutyl 1,2-cyclohexanedicarboxylate-   (2) (isobutyl)(2-ethylhexyl) 1,2-cyclohexanedicarboxylate-   (3) di(2-ethylhexyl) 1,2-cyclohexanedicarboxylate    -   (1)/(2)/(3)=20.4/43.6/36.0 (area %)

Example II-16

In the same manner as in Example II-15, a reaction was conducted using154.1 g (1 mole) of 1,2-cyclohexanedicarboxylic anhydride (prepared byhydrogenating 4-cyclohexene-1,2-dicarboxylic anhydride obtained by usualDiels-Alder reaction of maleic anhydride and 1,3-butadiene) and 74 g (1mole) of isobutanol with a peroxide value of 0.1 meq/kg and a carbonylvalue of 0.1 as alcohol component 1, whereby the total acid number ofthe reaction mixture became 246 mgKOH/g (theoretical value: 246mgKOH/g).

Then, to the reaction mixture was added tin oxide (0.2 wt. % based onthe starting materials fed), and at 220° C., 56.2 g (0.76 mole) of saidisobutanol and 57.2 g (0.44 mole) of 2-ethylhexanol with a peroxidevalue of 0.2 meq/kg and a carbonyl value of 0.1 as alcohol component 2were further added dropwise. While water generated during the reactionwas removed by water separator, the esterification reaction was carriedout at 220° C. for about 9 hours until the total acid number of thereaction mixture became 3 mgKOH/g or less, and further continued at 220C and at 20000 Pa for 1 hour.

After the reaction, the excess alcohols were removed by distillation at180° C. under a reduced pressure of 1330 Pa, and the obtained liquidresidue was neutralized by adding thereto 27 g of a 4% aqueous solutionof sodium hydroxide and stirring the mixture at 80° C. for 2 hours, andthen washed with water until it became neutral, giving a crude estermixture. At this point, the crude ester mixture had a total acid numberof 0.01 mgKOH/g. Subsequently, to the crude ester mixture was addedactivated carbon (“Shirasagi M” manufactured by Sumitomo Chemical Co.,Ltd.; 0.1 wt. % based on the starting materials fed), and the mixturewas stirred at 90° C. and at 1330 Pa for 1 hour and filtered, whereby308 g of a purified ester mixture containing (isobutyl) (2-ethylhexyl)1,2-cyclohexanedicarboxylate was obtained. Dehydration was carried outat 100° C. under a reduced pressure of 1330 Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 6. The ester mixture had a water content of13 ppm, a sulfated ash content of 1 ppm, a sulfur content of less than 1ppm, a phosphorus content of less than 1 ppm, a hydroxyl value of 1.0mgKOH/g, a peroxide value of 0.2 meq/kg and a carbonyl value of 0.1. Theobtained ester mixture had a cis:trans isomer ratio of 28:72 (area %),as determined from the gas chromatogram thereof. Further, the obtainedester mixture was found to be a mixture of the following esters from thegas chromatogram thereof:

-   (1) diisobutyl 1,2-cyclohexanedicarboxylate-   (2) (isobutyl) (2-ethylhexyl) 1,2-cyclohexanedicarboxylate-   (3) di(2-ethylhexyl) 1,2-cyclohexanedicarboxylate    -   (1)/(2)/(3)=60.7/33.4/5.9 (area %)

Example II-17

In the same manner as in Example II-15, a reaction was carried out using154.1 g (1 mole) of 1,2-cyclohexanedicarboxylic anhydride (prepared byhydrogenating 4-cyclohexene-1,2-dicarboxylic anhydride obtained by usualDiels-Alder reaction of maleic anhydride and 1,3-butadiene) and 74 g (1mole) of n-butanol with a peroxide value of 0.2 meq/kg and a carbonylvalue of 0.1 as alcohol component 1, whereby the total acid number ofthe reaction mixture became 246 mgKOH/g (theoretical value: 246mgKOH/g).

Then, to the reaction mixture was added tin oxide (0.2 wt. % based onthe starting materials fed) as a catalyst as a catalyst, and at 220° C.,7.4 g (0.1 mole) of said n-butanol and 173.8 g (1.1 moles) of isodecanolwith a peroxide value of 0.1 meq/kg and a carbonyl value of 0.3 asalcohol component 2 were further added dropwise. While water generatedduring the reaction was removed by water separator, the esterificationreaction was carried out at 220° C. for about 9 hours until the totalacid number of the reaction mixture became 3 mgKOH/g or less, andfurther continued at 220° C. and at 20000 Pa for 1 hour.

After the reaction, the excess alcohols were removed by distillation at180° C. under a reduced pressure of 1330 Pa, and the obtained liquidresidue was neutralized by adding thereto 27 g of a 4% aqueous solutionof sodium hydroxide and stirring the mixture at 80° C. for 2 hours, andthen washed with water until it became neutral, giving a crude estermixture. At this point, the crude ester mixture had a total acid numberof 0.01 mgKOH/g. Subsequently, to the crude ester mixture was addedactivated carbon (“Shirasagi M” manufactured by Sumitomo Chemical Co.,Ltd.; 0.1 wt. % based on the starting materials fed), and the mixturewas stirred at 90° C. and at 1330 Pa for 1 hour and filtered, whereby317 g of a purified ester mixture containing (n-butyl)(isodecyl)1,2-cyclohexanedicarboxylate was obtained. Dehydration was carried outat 100° C. under a reduced pressure of 1330 Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 6. The ester mixture had a water content of15 ppm, a sulfated ash content of less than 1 ppm, a sulfur content ofless than 1 ppm, a phosphorus content of less than 1 ppm, a hydroxylvalue of 0.5 mgKOH/g, a peroxide value of 0.3 meq/kg and a carbonylvalue of 0.4. The obtained ester mixture had a cis:trans isomer ratio of48:52 (area %), as determined from the gas chromatogram thereof.Further, the obtained ester mixture was found to be a mixture of thefollowing esters from the gas chromatogram thereof:

-   (1) di(n-butyl) 1,2-cyclohexanedicarboxylate-   (2) (n-butyl)(isodecyl) 1,2-cyclohexanedicarboxylate-   (3) diisodecyl 1,2-cyclohexanedicarboxylate    -   (1)/(2)/(3)=19.7/46.8/32.5 (area %)

Example II-18

In the same manner as in Example II-15, a reaction was carried out using154.1 g (1 mole) of 1,2-cyclohexanedicarboxylic anhydride (prepared byhydrogenating 4-cyclohexene-1,2-dicarboxylic anhydride obtained by usualDiels-Alder reaction of maleic anhydride and 1,3-butadiene) and 74 g (1mole) of isobutanol with a peroxide value of 0.1 meq/kg and a carbonylvalue of 0.1 as alcohol component 1, whereby the total acid number ofthe reaction mixture became 246 mgKOH/g (theoretical value: 246mgKOH/g).

Then, to the reaction mixture was added tin oxide (0.2 wt. % based onthe starting materials fed) as a catalyst, and at 220° C., 7.4 g (0.1mole) of said isobutanol and 158.4 g (1.1 moles) of3,5,5-trimethylhexanol with a peroxide value of 0.1 meq/kg and acarbonyl value of 0.2 as alcohol component 2 were further addeddropwise. While water generated during the reaction was removed by waterseparator, the esterification reaction was carried out at 220° C. forabout 9 hours until the total acid number of the reaction mixture became3 mgKOH/g or less, and further continued at 220° C. and at 20000 Pa for1 hour.

After the reaction, the excess alcohols were removed by distillation at180° C. under a reduced pressure of 1330 Pa, and the obtained liquidresidue was neutralized by adding thereto 27 g of a 4% aqueous solutionof sodium hydroxide and stirring the mixture at 80° C. for 2 hours, andthen washed with water until it became neutral, giving a crude estermixture. At this point, the crude ester mixture had a total acid numberof 0.01 mgKOH/g. Subsequently, to the crude ester mixture was addedactivated carbon (“Shirasagi M” manufactured by Sumitomo Chemical Co.,Ltd.; 0.1 wt. % based on the starting materials fed), and the mixturewas stirred at 90° C. and at 1330 Pa for 1 hour and filtered, whereby320 g of a purified ester mixture containing(isobutyl)(3,5,5-trimethylhexyl) 1,2-cyclohexanedicarboxylate wasobtained. Dehydration was carried out at 100° C. under a reducedpressure of 1330 Pa for 6 hours. The total acid number and kinematicviscosity of the obtained ester are shown in Table 6.

The ester mixture had a water content of 12 ppm, a sulfated ash contentof less than 1 ppm, a sulfur content of less than 1 ppm, a phosphoruscontent of less than 1 ppm, a hydroxyl value of 0.2 mgKOH/g, a peroxidevalue of 0.1 meq/kg and a carbonyl value of 0.2. The obtained estermixture had a cis:trans isomer ratio of 38:62 (area %), as determinedfrom the gas chromatogram thereof. Further, the obtained ester mixturewas found to be a mixture of the following esters from the gaschromatogram thereof:

-   (1) diisobutyl 1,2-cyclohexanedicarboxylate-   (2) (isobutyl)(3,5,5-trimethylhexyl) 1,2-cyclohexanedicarboxylate-   (3) di(3,5,5-trimethylhexyl) 1,2-cyclohexanedicarboxylate    -   (1)/(2)/(3)=21.9/44.2/33.9 (area %)

Example II-19

In the same manner as in Example II-15, 148 g (1 mole) of phthalicanhydride was reacted with 74 g (1 mole) of isobutanol with a peroxidevalue of 0.1 meq/kg and a carbonyl value of 0.1 as alcohol component 1,whereby the total acid number of the reaction mixture became 254 mgKOH/g(theoretical value: 252 mgKOH/g).

Then, to the reaction mixture was added tin oxide (0.2 wt. % based onthe starting materials fed) as a catalyst, and at 220° C., 7.4 g (0.1mole) of said isobutanol and 143 g (1.1 moles) of 2-ethylhexanol with aperoxide value of 0.2 meq/kg and a carbonyl value of 0.1 as alcoholcomponent 2 were further added dropwise. While water generated duringthe reaction was removed by water separator, the esterification reactionwas carried out at 220° C. for about 6 hours until the total acid numberof the reaction mixture became 3 mgKOH/g or less, and further continuedat 220° C. and at 20000 Pa for 1 hour.

After the reaction, the excess alcohols were removed by distillation at180° C. under a reduced pressure of 1330 Pa, and the obtained liquidresidue was neutralized by adding thereto 27 g of a 4% aqueous solutionof sodium hydroxide and stirring the mixture at 80° C. for 2 hours, andthen washed with water until it became neutral, giving a crude estermixture. At this point, the crude ester mixture had a total acid numberof 0.01 mgKOH/g. Subsequently, to the crude ester mixture was addedactivated carbon (“Shirasagi M” manufactured by Sumitomo Chemical Co.,Ltd.; 0.1 wt. % based on the starting materials fed), and the mixturewas stirred at 90° C. and at 1330 Pa for 1 hour and filtered, whereby320 g of a purified ester mixture containing (isobutyl) (2-ethylhexyl)phthalate was obtained. Dehydration was carried out at 100° C. under areduced pressure of 1330 Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 6. The ester mixture had a water content of25 ppm, a sulfated ash content of less than 1 ppm, a sulfur content ofless than 1 ppm, a phosphorus content of less than 1 ppm, a hydroxylvalue of 0.2 mgKOH/g, a peroxide value of 0.1 meq/kg and a carbonylvalue of 0.1. The obtained ester mixture was found to be a mixture ofthe following esters from the gas chromatogram thereof:

-   (1) diisobutyl phthalate-   (2) (isobutyl) (2-ethylhexyl) phthalate-   (3) di(2-ethylhexyl) phthalate    -   (1)/(2)/(3)=21.1/40.8/38.1 (area %)

Example II-20

In the same manner as in Example II-15, 148 g (1 mole) of phthalicanhydride was reacted with 74 g (1 mole) of isobutanol with a peroxidevalue of 0.1 meq/kg and a carbonyl value of 0.1 as alcohol component 1,whereby the total acid number of the reaction mixture became 252 mgKOH/g(theoretical value: 252 mgKOH/g).

Then, to the reaction mixture was added tin oxide (0.2 wt. % based onthe starting materials fed) as a catalyst, and at 220° C., 7.4 g (0.1mole) of said isobutanol and 158.4 g (1.1 moles) of3,5,5-trimethylhexanol with a peroxide value of 0.1 meq/kg and acarbonyl value of 0.2 as alcohol component 2 were further addeddropwise. While water generated during the reaction was removed by waterseparator, the esterification reaction was carried out at 220° C. forabout 6 hours until the total acid number of the reaction mixture became3 mgKOH/g or less, and further continued at 220° C. and at 20000 Pa for1 hour.

After the reaction, the excess alcohols were removed by distillation at180° C. under a reduced pressure of 1330 Pa, and the obtained liquidresidue was neutralized by adding thereto 30 g of a 4% aqueous solutionof sodium hydroxide and stirring the mixture at 80° C. for 2 hours, andthen washed with water until it became neutral, giving a crude estermixture. At this point, the crude ester mixture had a total acid numberof 0.01 mgKOH/g.

Subsequently, to the crude ester mixture was added activated carbon(“Shirasagi M” manufactured by Sumitomo Chemical Co., Ltd.; 0.1 wt. %based on the starting materials fed), and the mixture was stirred at 90°C. and at 1330 Pa for 1 hour and filtered, whereby 329 g of a purifiedester mixture containing (isobutyl) (3,5,5-trimethylhexyl) phthalate wasobtained. Dehydration was carried out at 100° C. under a reducedpressure of 1330 Pa for 6 hours.

The total acid number and kinematic viscosity of the obtained estermixture are shown in Table 6. The ester mixture had a water content of11 ppm, a sulfated ash content of less than 1 ppm, a sulfur content ofless than 1 ppm, a phosphorus content of less than 1 ppm, a hydroxylvalue of 1.4 mgKOH/g, a peroxide value of 0.2 meq/kg and a carbonylvalue of 0.2. The obtained ester mixture was found to be a mixture ofthe following esters from the gas chromatogram thereof:

-   (1) diisobutyl phthalate-   (2) (isobutyl)(3,5,5-trimethylhexyl) phthalate-   (3) di(3,5,5-trimethylhexyl) phthalate

(1)/(2)/(3)=21.9/44.2/33.9 (area %) TABLE 6 Properties of esters TotalKinematic acid viscosity Ex. Acid component Alcohol component number 40°C. 100° C. II-7  4-Cyclohexene-1,2- Isobutanol (45 mole %)/ 0.01 13.02.7 dicarboxylic acid 2-Ethylhexanol (55 mole %) II-8 4-Cyclohexene-1,2- Isobutanol (18 mole %)/ 0.01 15.2 3.1 dicarboxylicacid 2-Ethylhexanol (82 mole %) II-9  4-Cyclohexene-1,2- Isobutanol (85mole %)/ 0.01 9.3 2.2 dicarboxylic acid 2-Ethylhexanol (15 mole %) II-104-Cyclohexene-1,2- Isobutanol (50 mole %)/ 0.01 12.0 2.6 dicarboxylicacid 2-Ethylhexanol (50 mole %) II-11 4-Cyclohexene-1,2- Isobutanol (32mole %)/ 0.01 16.5 3.3 dicarboxylic acid Isononanol (68 mole %) II-124-Cyclohexene-1,2- Isobutanol (50 mole %)/3,5,5- 0.01 16.0 3.1dicarboxylic acid Trimethylhexanol (50 mole %) II-13 4-Cyclohexene-1,2-Isobutanol (20 mole %)/3,5,5- 0.01 22.6 4.0 dicarboxylic acidtrimethylhexanol (80 mole %) II-14 1,2-Cyclohexane- Isobutanol (45 mole%)/ 0.01 12.9 2.7 dicarboxylic acid 2-Ethylhexanol (55 mole %) II-151,2-Cyclohexane- Isobutanol (50 mole %)/ 0.01 12.7 2.6 dicarboxylic acid2-Ethylhexanol (50 mole %) II-16 1,2-Cyclohexane- Isobutanol (80 mole%)/ 0.01 10.1 2.3 dicarboxylic acid 2-Ethylhexanol (20 mole %) II-171,2-Cyclohexane- n-Butanol (50 mole %)/ 0.01 12.5 2.8 dicarboxylic acidIsodecanol (50 mole %) II-18 1,2-Cyclohexane- Isobutanol (50 mole%)/3,5,5- 0.01 17.3 3.3 dicarboxylic acid trimethylhexanol (50 mole %)II-19 Phthalic acid Isobutanol (50 mole %)/ 0.01 20.3 3.4 2-Ethylhexanol(50 mole %) II-20 Phthalic acid Isobutanol (50 mole %)/3,5,5- 0.01 25.04.0 trimethylhexanol (50 mole %)*Total acid number: mgKOH/g*Kinematic viscosity: mm²/s

Test Example II-1

The hydrolysis stability was evaluated with respect to the estermixtures of Examples II-1 to II-18 and Comparative Examples II-1 andII-2. The results are shown in Table 7.

Test Example II-2

The heat stability was evaluated with respect to the ester mixtures ofExamples II-1 to II-18 and Comparative Examples II-1 and II-2. Theresults are shown in Table 7.

Test Example II-3

The electrical insulating property was evaluated in terms of volumeresistivity with respect to the ester mixtures of Examples II-1 to II-18and Comparative Examples II-1 and II-2. The results are shown in Table7. TABLE 7 Hydrolysis stability, Heat stability and Electricalinsulating property Heat Hydrolysis stability stability Total acid Totalacid number Volume number after after test resistivity Sample test(mgKOH/g) (mgKOH/g) (Ω · cm) Ester of Ex. II-1 0.70 0.69 2.6 × 10¹²Ester of Ex. II-2 0.66 0.65 4.0 × 10¹² Ester of Ex. II-3 0.81 0.65 1.0 ×10¹² Ester of Ex. II-4 0.75 0.68 2.5 × 10¹² Ester of Ex. II-5 0.82 0.605.3 × 10¹² Ester of Ex. II-6 0.66 0.81 2.0 × 10¹² Ester of Comp. Ex.II-1 3.15 2.15 4.0 × 10¹¹ Ester of Comp. Ex. II-2 1.84 1.88 7.3 × 10¹¹Ester of Ex. II-7 0.26 0.45 8.6 × 10¹² Ester of Ex. II-8 0.25 0.49 3.0 ×10¹³ Ester of Ex. II-9 0.33 0.42 6.3 × 10¹² Ester of Ex. II-10 0.30 0.519.0 × 10¹² Ester of Ex. II-11 0.36 0.45 8.3 × 10¹² Ester of Ex. II-120.35 0.48 3.0 × 10¹³ Ester of Ex. II-13 0.39 0.57 3.6 × 10¹³ Ester ofEx. II-14 0.28 0.62 1.7 × 10¹³ Ester of Ex. II-15 0.31 0.73 9.7 × 10¹²Ester of Ex. II-16 0.37 0.80 6.9 × 10¹² Ester of Ex. II-17 0.64 0.85 7.0× 10¹² Ester of Ex. II-18 0.38 0.77 2.0 × 10¹³ Ester of Ex. II-19 0.880.33 1.4 × 10¹² Ester of Ex. II-20 0.98 0.27 4.0 × 10¹²

As apparent from Examples II-1 to II-6, the alicyclic adjacentdicarboxylic acid mixed diesters prepared by the process of the presentinvention are excellent in hydrolysis stability, heat stability andelectrical insulating property.

On the other hand, the alicyclic adjacent dicarboxylic acid mixeddiesters prepared by one-step process as described in ComparativeExamples II-1 and II-2 are poor in hydrolysis stability and heatstability, since they exhibit a great increase in total acid number, andare also low in volume resistivity. Esters prepared by using asulfur-containing catalyst are also inferior in these properties.

Furthermore, Examples II-7 to II-20 demonstrate that the alicyclic oraromatic adjacent dicarboxylic acid mixed diesters prepared by using analcohol low in peroxide value and carbonyl value display notably highhydrolysis stability and heat stability, and are more excellent as arefrigerator oil.

1. An ester selected from the group consisting of alicyclic or aromaticdicarboxylic acid diesters represented by the formula (E)

wherein A represents a cyclohexane ring, a cyclohexene ring or a benzenering, X is a hydrogen atom or methyl, R^(X) and R^(Y) are the same ordifferent and each is a branched-chain alkyl group having 3 to 18 carbonatoms, a straight-chain alkyl group having 1 to 18 carbon atoms, astraight-chain alkenyl group having 2 to 18 carbon atoms or a cycloalkylgroup having 3 to 10 carbon atoms, provided that when A is a benzenering, R^(X) and R^(Y) are different from each other and the group—COOR^(X) and the group —COOR^(Y) are attached to adjacent two carbonatoms of the benzene ring, the ester having the following properties: 1)a total acid number of 0.05 mgKOH/g or less, 2) a sulfated ash contentof 10 ppm or less, 3) a sulfur content of 20 ppm or less, 4) aphosphorus content of 20 ppm or less, 5) a peroxide value of 1.0 meq/kgor less, 6) a carbonyl value of 10 or less, 7) a volume resistivity of1×10¹¹ Ω·cm or more, 8) a hydroxyl value of 3 mgKOH/g or less, and 9) awater content of 100 ppm or less.
 2. An ester selected from the groupconsisting of (I) alicyclic dicarboxylic acid diesters represented bythe formula (1)

wherein A¹ represents a cyclohexane ring or cyclohexene ring, X is ahydrogen atom or methyl, R¹ and R² are the same or different and each isa branched-chain alkyl group having 3 to 18 carbon atoms, astraight-chain alkyl group having 1 to 18 carbon atoms, a straight-chainalkenyl group having 2 to 18 carbon atoms or a cycloalkyl group having 3to 10 carbon atoms; and (II) alicyclic or aromatic adjacent dicarboxylicacid mixed diesters represented by the formula (4)

wherein A represents a cyclohexane ring, a cyclohexene ring or a benzenering, X is a hydrogen atom or methyl, R⁵ and R⁶ are different from eachother and each is a branched-chain alkyl group having 3 to 18 carbonatoms, a straight-chain alkyl group having 1 to 18 carbon atoms, astraight-chain alkenyl group having 2 to 18 carbon atoms or a cycloalkylgroup having 3 to 10 carbon atoms, and the group —COOR⁵ and the group—COOR⁶ are attached to two adjacent carbon atoms of the cyclohexanering, cyclohexene ring or benzene ring represented by A, the esterhaving the following properties: 1) a total acid number of 0.05 mgKOH/gor less, 2) a sulfated ash content of 10 ppm or less, 3) a sulfurcontent of 20 ppm or less, 4) a phosphorus content of 20 ppm or less, 5)a peroxide value of 1.0 meq/kg or less, 6) a carbonyl value of 10 orless, 7) a volume resistivity of 1×10¹¹ Ω·cm or more, 8) a hydroxylvalue of 3 mgKOH/g or less, and 9) a water content of 100 ppm or less.3. An alicyclic dicarboxylic acid diester represented by the formula (1)

wherein A¹ represents a cyclohexane ring or cyclohexene ring, X is ahydrogen atom or methyl, R¹ and R² are the same or different and each isa branched-chain alkyl group having 3 to 18 carbon atoms, astraight-chain alkyl group having 1 to 18 carbon atoms, a straight-chainalkenyl group having 2 to 18 carbon atoms or a cycloalkyl group having 3to 10 carbon atoms; the alicyclic dicarboxylic acid diester having thefollowing properties: 1) a total acid number of 0.05 mgKOH/g or less, 2)a sulfated ash content of 10 ppm or less, 3) a sulfur content of 20 ppmor less, 4) a phosphorus content of 20 ppm or less, 5) a peroxide valueof 1.0 meq/kg or less, 6) a carbonyl value of 10 or less, 7) a volumeresistivity of 1×10¹¹ Ω·cm or more, 8) a hydroxyl value of 3 mgKOH/g orless, and 9) a water content of 100 ppm or less.
 4. The alicyclicdicarboxylic acid diester according to claim 3 wherein A¹ is acyclohexane ring and X is a hydrogen atom, or A¹ is a cyclohexene ringand X is a hydrogen atom, or A¹ is a cyclohexene ring and X is methyl,and the two ester groups —COOR¹ and —COOR² are attached to 1- and2-positions of the cyclohexane ring or cyclohexene ring represented byA¹.
 5. The alicyclic dicarboxylic acid diester according to claim 4wherein R¹ and R² are the same and each represents straight-chain orbranched-chain alkyl group having 3 to 11 carbon atoms, A¹ is acyclohexane ring or cyclohexene ring and X is a hydrogen atom. 6-13.(canceled).
 14. An alicyclic or aromatic adjacent dicarboxylic acidmixed diester represented by the formula (4)

wherein A represents a cyclohexane ring, a cyclohexene ring or a benzenering, X is a hydrogen atom or methyl, R⁵ and R⁶ are different from eachother and each is a branched-chain alkyl group having 3 to 18 carbonatoms, a straight-chain alkyl group having 1 to 18 carbon atoms, astraight-chain alkenyl group having 2 to 18 carbon atoms or a cycloalkylgroup having 3 to 10 carbon atoms, and the group —COOR⁵ and the group—COOR⁶ are attached to two adjacent carbon atoms of the cyclohexanering, cyclohexene ring or benzene ring represented by A; and having thefollowing properties: 1) a total acid number of 0.05 mgKOH/g or less, 2)a sulfated ash content of 10 ppm or less, 3) a sulfur content of 20 ppmor less, 4) a phosphorus content of 20 ppm or less, 5) a peroxide valueof 1.0 meq/kg or less, 6) a carbonyl value of 10 or less, 7) a volumeresistivity of 1×10¹¹ Ω·cm or more, 8) a hydroxyl value of 3 mgKOH/g orless, and 9) a water content of 100 ppm or less.
 15. An alicyclic oraromatic adjacent dicarboxylic acid mixed diester according to claim 14wherein A is a cyclohexane ring or cyclohexene ring, X is a hydrogenatom, R⁵ is a straight-chain alkyl group having 1 to 5 carbon atoms or abranched-chain alkyl group having 3 to 5 carbon atoms, and R⁶ is astraight-chain or branched chain alkyl group having 6 to 11 carbonatoms, and when A is a cyclohexene ring, the group —COOR⁵ and group—COOR⁶ are present at the 1- and 2-positions and the double bond ispresent between the 4- and 5-positions.
 16. An ester mixture of (1) analicyclic or aromatic adjacent dicarboxylic acid di(lower alkyl)esterrepresented by the formula (7)

wherein A represents a cyclohexane ring, a cyclohexene ring or a benzenering, X is a hydrogen atom or methyl and R^(5a) is a branched-chainalkyl group having 3 to 5 carbon atoms, a straight-chain alkyl grouphaving 1 to 5 carbon atoms, a straight-chain alkenyl group having 2 to 5carbon atoms or a cycloalkyl group having 3 to 5 carbon atoms, and thetwo COOR^(5a) groups are the same and attached to two adjacent carbonatoms of the cyclohexane ring, cyclohexene ring or benzene ringrepresented by A; (2) an alicyclic or aromatic adjacent dicarboxylicacid mixed diester represented by the formula (4a)

wherein A and X are as defined in the formula (7), and R^(5a) and R^(6a)are different from each other and R^(5a) is as defined in the formula(7), and R^(6a) is a branched-chain alkyl group having 6 to 18 carbonatoms, a straight-chain alkyl group having 6 to 18 carbon atoms, astraight-chain alkenyl group having 6 to 18 carbon atoms or a cycloalkylgroup having 6 to 10 carbon atoms, and the group —COOR^(5a) and thegroup —COOR^(6a) are attached to two adjacent carbon atoms of thecyclohexane ring, cyclohexene ring or benzene ring represented by A, and(3) an alicyclic or aromatic adjacent dicarboxylic acid di(higheralkyl)ester represented by the formula (8)

wherein A, X and R^(6a) are as defined in the formula (4a), and the two—COOR^(6a) groups are the same and attached to two adjacent carbon atomsof the cyclohexane ring, cyclohexene ring or benzene ring represented byA, the ester mixture having the following properties: 1) a total acidnumber of 0.05 mgKOH/g or less, 2) a sulfated ash content of 10 ppm orless, 3) a sulfur content of 20 ppm or less, 4) a phosphorus content of20 ppm or less, 5) a peroxide value of 1.0 meq/kg or less, 6) a carbonylvalue of 10 or less, 7) a volume resistivity of 1×10¹¹ Ω·cm or more, 8)a hydroxyl value of 3 mgKOH/g or less, and 9) a water content of 100 ppmor less.
 17. The ester mixture according to claim 16 wherein thealicyclic or aromatic adjacent dicarboxylic acid mixed diesterrepresented by the formula (4a) under (2) is present in a proportion of100, the alicyclic or aromatic adjacent dicarboxylic acid di(loweralkyl) ester represented by the formula (7) under (1) is present in aproportion of 5-300, and the alicyclic or aromatic adjacent dicarboxylicacid di(higher alkyl)ester under (3) is present in a proportion of7-500, wherein the proportions are expressed in terms of area ratio asdetermined from a gas chromatogram of the ester mixture.
 18. The estermixture according to claim 16 wherein the ester mixture is a mixture ofan alicyclic adjacent dicarboxylic acid di(lower alkyl)ester representedby the formula (7), an alicyclic adjacent dicarboxylic acid mixeddiester represented by the formula (4a) and an alicyclic adjacentdicarboxylic acid di(higher alkyl)ester represented by the formula (8),the ester mixture having a trans isomer/cis isomer ratio of 0/100 to80/20 (by area % as determined by gas chromatography). 19-32.(canceled).